Bug 1355351 - Make pseudo-elements return the correct style via getComputedStyle

* Add a node property to access the ::before and ::after pseudo-elements
* Look for the frame for ::before and ::after pseudos
* Clean up pseudo-element props
* Simplify nsLayoutUtils callers, and make child iterators notice display: contents pseudos

Tag #1375

16 files changed, 188 insertions, 241 deletions

diff --git a/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js b/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js
index 9ca5451a56..7c18bfe7bf 100644
--- a/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js
+++ b/devtools/client/inspector/computed/test/browser_computed_pseudo-element_01.js
@@ -33,7 +33,7 @@ function* testTopLeft(inspector, view) {
   let afterElement = children.nodes[children.nodes.length - 1];
   yield selectNode(afterElement, inspector);
   top = getComputedViewPropertyValue(view, "top");
-  is(top, "50%", "The computed view shows the correct top");
+  is(top, "96px", "The computed view shows the correct top");
   left = getComputedViewPropertyValue(view, "left");
-  is(left, "50%", "The computed view shows the correct left");
+  is(left, "96px", "The computed view shows the correct left");
 }
diff --git a/dom/animation/EffectCompositor.cpp b/dom/animation/EffectCompositor.cpp
index c88cabe90b..49da3c0332 100644
--- a/dom/animation/EffectCompositor.cpp
+++ b/dom/animation/EffectCompositor.cpp
@@ -356,24 +356,16 @@ EffectCompositor::GetElementToRestyle(dom::Element* aElement,
     return aElement;
   }
 
-  nsIFrame* primaryFrame = aElement->GetPrimaryFrame();
-  if (!primaryFrame) {
-    return nullptr;
-  }
-  nsIFrame* pseudoFrame;
   if (aPseudoType == CSSPseudoElementType::before) {
-    pseudoFrame = nsLayoutUtils::GetBeforeFrame(primaryFrame);
-  } else if (aPseudoType == CSSPseudoElementType::after) {
-    pseudoFrame = nsLayoutUtils::GetAfterFrame(primaryFrame);
-  } else {
-    NS_NOTREACHED("Should not try to get the element to restyle for a pseudo "
-                  "other that :before or :after");
-    return nullptr;
+    return nsLayoutUtils::GetBeforePseudo(aElement);
   }
-  if (!pseudoFrame) {
-    return nullptr;
+  if (aPseudoType == CSSPseudoElementType::after) {
+    return nsLayoutUtils::GetAfterPseudo(aElement);
   }
-  return pseudoFrame->GetContent()->AsElement();
+
+  NS_NOTREACHED("Should not try to get the element to restyle for a pseudo "
+                "other that :before or :after");
+  return nullptr;
 }
 
 bool
diff --git a/dom/animation/KeyframeEffectReadOnly.cpp b/dom/animation/KeyframeEffectReadOnly.cpp
index 639e0b2b0d..164ee02925 100644
--- a/dom/animation/KeyframeEffectReadOnly.cpp
+++ b/dom/animation/KeyframeEffectReadOnly.cpp
@@ -1105,19 +1105,17 @@ KeyframeEffectReadOnly::GetAnimationFrame() const
     return nullptr;
   }
 
-  nsIFrame* frame = mTarget->mElement->GetPrimaryFrame();
-  if (!frame) {
-    return nullptr;
-  }
-
+  nsIFrame* frame;
   if (mTarget->mPseudoType == CSSPseudoElementType::before) {
-    frame = nsLayoutUtils::GetBeforeFrame(frame);
+    frame = nsLayoutUtils::GetBeforeFrame(mTarget->mElement);
   } else if (mTarget->mPseudoType == CSSPseudoElementType::after) {
-    frame = nsLayoutUtils::GetAfterFrame(frame);
+    frame = nsLayoutUtils::GetAfterFrame(mTarget->mElement);
   } else {
+    frame = mTarget->mElement->GetPrimaryFrame();
     MOZ_ASSERT(mTarget->mPseudoType == CSSPseudoElementType::NotPseudo,
                "unknown mTarget->mPseudoType");
   }
+
   if (!frame) {
     return nullptr;
   }
diff --git a/dom/base/ChildIterator.cpp b/dom/base/ChildIterator.cpp
index fb07e9a210..23b919516b 100644
--- a/dom/base/ChildIterator.cpp
+++ b/dom/base/ChildIterator.cpp
@@ -317,11 +317,9 @@ AllChildrenIterator::Get() const
 {
   switch (mPhase) {
     case eAtBeforeKid: {
-      nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-      MOZ_ASSERT(frame, "No frame at eAtBeforeKid phase");
-      nsIFrame* beforeFrame = nsLayoutUtils::GetBeforeFrame(frame);
-      MOZ_ASSERT(beforeFrame, "No content before frame at eAtBeforeKid phase");
-      return beforeFrame->GetContent();
+      Element* before = nsLayoutUtils::GetBeforePseudo(mOriginalContent);
+      MOZ_ASSERT(before, "No content before frame at eAtBeforeKid phase");
+      return before;
     }
 
     case eAtExplicitKids:
@@ -331,11 +329,9 @@ AllChildrenIterator::Get() const
       return mAnonKids[mAnonKidsIdx];
 
     case eAtAfterKid: {
-      nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-      MOZ_ASSERT(frame, "No frame at eAtAfterKid phase");
-      nsIFrame* afterFrame = nsLayoutUtils::GetAfterFrame(frame);
-      MOZ_ASSERT(afterFrame, "No content before frame at eAtBeforeKid phase");
-      return afterFrame->GetContent();
+      Element* after = nsLayoutUtils::GetAfterPseudo(mOriginalContent);
+      MOZ_ASSERT(after, "No content after frame at eAtAfterKid phase");
+      return after;
     }
 
     default:
@@ -349,15 +345,10 @@ AllChildrenIterator::Seek(nsIContent* aChildToFind)
 {
   if (mPhase == eAtBegin || mPhase == eAtBeforeKid) {
     mPhase = eAtExplicitKids;
-    nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-    if (frame) {
-      nsIFrame* beforeFrame = nsLayoutUtils::GetBeforeFrame(frame);
-      if (beforeFrame) {
-        if (beforeFrame->GetContent() == aChildToFind) {
-          mPhase = eAtBeforeKid;
-          return true;
-        }
-      }
+    Element* beforePseudo = nsLayoutUtils::GetBeforePseudo(mOriginalContent);
+    if (beforePseudo && beforePseudo == aChildToFind) {
+      mPhase = eAtBeforeKid;
+      return true;
     }
   }
 
@@ -404,13 +395,10 @@ AllChildrenIterator::GetNextChild()
 {
   if (mPhase == eAtBegin) {
     mPhase = eAtExplicitKids;
-    nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-    if (frame) {
-      nsIFrame* beforeFrame = nsLayoutUtils::GetBeforeFrame(frame);
-      if (beforeFrame) {
-        mPhase = eAtBeforeKid;
-        return beforeFrame->GetContent();
-      }
+    Element* beforeContent = nsLayoutUtils::GetBeforePseudo(mOriginalContent);
+    if (beforeContent) {
+      mPhase = eAtBeforeKid;
+      return beforeContent;
     }
   }
 
@@ -446,13 +434,10 @@ AllChildrenIterator::GetNextChild()
       return mAnonKids[mAnonKidsIdx];
     }
 
-    nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-    if (frame) {
-      nsIFrame* afterFrame = nsLayoutUtils::GetAfterFrame(frame);
-      if (afterFrame) {
-        mPhase = eAtAfterKid;
-        return afterFrame->GetContent();
-      }
+    Element* afterContent = nsLayoutUtils::GetAfterPseudo(mOriginalContent);
+    if (afterContent) {
+      mPhase = eAtAfterKid;
+      return afterContent;
     }
   }
 
@@ -466,13 +451,10 @@ AllChildrenIterator::GetPreviousChild()
   if (mPhase == eAtEnd) {
     MOZ_ASSERT(mAnonKidsIdx == mAnonKids.Length());
     mPhase = eAtAnonKids;
-    nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-    if (frame) {
-      nsIFrame* afterFrame = nsLayoutUtils::GetAfterFrame(frame);
-      if (afterFrame) {
-        mPhase = eAtAfterKid;
-        return afterFrame->GetContent();
-      }
+    Element* afterContent = nsLayoutUtils::GetAfterPseudo(mOriginalContent);
+    if (afterContent) {
+      mPhase = eAtAfterKid;
+      return afterContent;
     }
   }
 
@@ -501,13 +483,10 @@ AllChildrenIterator::GetPreviousChild()
       return kid;
     }
 
-    nsIFrame* frame = mOriginalContent->GetPrimaryFrame();
-    if (frame) {
-      nsIFrame* beforeFrame = nsLayoutUtils::GetBeforeFrame(frame);
-      if (beforeFrame) {
-        mPhase = eAtBeforeKid;
-        return beforeFrame->GetContent();
-      }
+    Element* beforeContent = nsLayoutUtils::GetBeforePseudo(mOriginalContent);
+    if (beforeContent) {
+      mPhase = eAtBeforeKid;
+      return beforeContent;
     }
   }
 
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 2ab5937ace..3f5b54c942 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -3657,11 +3657,11 @@ nsDOMWindowUtils::GetOMTAStyle(nsIDOMElement* aElement,
 
   RefPtr<nsROCSSPrimitiveValue> cssValue = nullptr;
   nsIFrame* frame = element->GetPrimaryFrame();
-  if (frame && !aPseudoElement.IsEmpty()) {
+  if (!aPseudoElement.IsEmpty()) {
     if (aPseudoElement.EqualsLiteral("::before")) {
-      frame = nsLayoutUtils::GetBeforeFrame(frame);
+      frame = nsLayoutUtils::GetBeforeFrame(element);
     } else if (aPseudoElement.EqualsLiteral("::after")) {
-      frame = nsLayoutUtils::GetAfterFrame(frame);
+      frame = nsLayoutUtils::GetAfterFrame(element);
     } else {
       return NS_ERROR_INVALID_ARG;
     }
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index c7c1197b1a..2f0e30387c 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -2144,12 +2144,14 @@ GK_ATOM(ongamepaddisconnected, "ongamepaddisconnected")
 #endif
 
 // Content property names
+GK_ATOM(afterPseudoProperty, "afterPseudoProperty")  // nsXMLElement*
 GK_ATOM(animationsProperty, "AnimationsProperty")        // FrameAnimations*
 GK_ATOM(animationsOfBeforeProperty, "AnimationsOfBeforeProperty") // FrameAnimations*
 GK_ATOM(animationsOfAfterProperty, "AnimationsOfAfterProperty") // FrameAnimations*
 GK_ATOM(animationEffectsProperty, "AnimationEffectsProperty") // EffectSet*
 GK_ATOM(animationEffectsForBeforeProperty, "AnimationsEffectsForBeforeProperty") // EffectSet*
 GK_ATOM(animationEffectsForAfterProperty, "AnimationsEffectsForAfterProperty") // EffectSet*
+GK_ATOM(beforePseudoProperty, "beforePseudoProperty")  // nsXMLElement*
 GK_ATOM(cssPseudoElementBeforeProperty, "CSSPseudoElementBeforeProperty") // CSSPseudoElement*
 GK_ATOM(cssPseudoElementAfterProperty, "CSSPseudoElementAfterProperty") // CSSPseudoElement*
 GK_ATOM(transitionsProperty, "TransitionsProperty")        // FrameTransitions*
diff --git a/dom/xml/nsXMLElement.cpp b/dom/xml/nsXMLElement.cpp
index 45163a1c42..ad0314f4ca 100644
--- a/dom/xml/nsXMLElement.cpp
+++ b/dom/xml/nsXMLElement.cpp
@@ -9,6 +9,7 @@
 #include "mozilla/dom/ElementInlines.h"
 #include "nsContentUtils.h" // nsAutoScriptBlocker
 
+using namespace mozilla;
 using namespace mozilla::dom;
 
 nsresult
@@ -29,4 +30,26 @@ nsXMLElement::WrapNode(JSContext *aCx, JS::Handle<JSObject*> aGivenProto)
   return ElementBinding::Wrap(aCx, this, aGivenProto);
 }
 
+void
+nsXMLElement::UnbindFromTree(bool aDeep, bool aNullParent)
+{
+  CSSPseudoElementType pseudoType = GetPseudoElementType();
+  bool isBefore = pseudoType == CSSPseudoElementType::before;
+  nsIAtom* property = isBefore
+    ? nsGkAtoms::beforePseudoProperty : nsGkAtoms::afterPseudoProperty;
+
+  switch (pseudoType) {
+    case CSSPseudoElementType::before:
+    case CSSPseudoElementType::after: {
+      MOZ_ASSERT(GetParent());
+      MOZ_ASSERT(GetParent()->IsElement());
+      GetParent()->DeleteProperty(property);
+      break;
+    }
+    default:
+      break;
+  }
+  Element::UnbindFromTree(aDeep, aNullParent);
+}
+
 NS_IMPL_ELEMENT_CLONE(nsXMLElement)
diff --git a/dom/xml/nsXMLElement.h b/dom/xml/nsXMLElement.h
index d16b82f399..85f79970cd 100644
--- a/dom/xml/nsXMLElement.h
+++ b/dom/xml/nsXMLElement.h
@@ -35,6 +35,9 @@ public:
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }
 
+  virtual void UnbindFromTree(bool aDeep = true,
+                              bool aNullParent = true) override;
+
 protected:
   virtual ~nsXMLElement() {}
 
diff --git a/layout/base/RestyleManager.cpp b/layout/base/RestyleManager.cpp
index 4d08dee067..8db3d93020 100644
--- a/layout/base/RestyleManager.cpp
+++ b/layout/base/RestyleManager.cpp
@@ -3626,14 +3626,14 @@ ElementRestyler::MustReframeForPseudo(CSSPseudoElementType aPseudoType,
     // Check for a ::before pseudo style and the absence of a ::before content,
     // but only if aFrame is null or is the first continuation/ib-split.
     if ((aFrame && !nsLayoutUtils::IsFirstContinuationOrIBSplitSibling(aFrame)) ||
-        nsLayoutUtils::GetBeforeFrameForContent(aGenConParentFrame, aContent)) {
+        nsLayoutUtils::GetBeforeFrame(aContent)) {
       return false;
     }
   } else {
     // Similarly for ::after, but check for being the last continuation/
     // ib-split.
     if ((aFrame && nsLayoutUtils::GetNextContinuationOrIBSplitSibling(aFrame)) ||
-        nsLayoutUtils::GetAfterFrameForContent(aGenConParentFrame, aContent)) {
+        nsLayoutUtils::GetAfterFrame(aContent)) {
       return false;
     }
   }
diff --git a/layout/base/ServoRestyleManager.cpp b/layout/base/ServoRestyleManager.cpp
index 9624c678be..0659ab8571 100644
--- a/layout/base/ServoRestyleManager.cpp
+++ b/layout/base/ServoRestyleManager.cpp
@@ -277,24 +277,17 @@ ServoRestyleManager::FrameForPseudoElement(const nsIContent* aContent,
                                            nsIAtom* aPseudoTagOrNull)
 {
   MOZ_ASSERT_IF(aPseudoTagOrNull, aContent->IsElement());
-  nsIFrame* primaryFrame = aContent->GetPrimaryFrame();
 
   if (!aPseudoTagOrNull) {
-    return primaryFrame;
-  }
-
-  if (!primaryFrame) {
-    return nullptr;
+    return aContent->GetPrimaryFrame();
   }
 
-  // NOTE: we probably need to special-case display: contents here. Gecko's
-  // RestyleManager passes the primary frame of the parent instead.
   if (aPseudoTagOrNull == nsCSSPseudoElements::before) {
-    return nsLayoutUtils::GetBeforeFrameForContent(primaryFrame, aContent);
+    return nsLayoutUtils::GetBeforeFrame(aContent);
   }
 
   if (aPseudoTagOrNull == nsCSSPseudoElements::after) {
-    return nsLayoutUtils::GetAfterFrameForContent(primaryFrame, aContent);
+    return nsLayoutUtils::GetAfterFrame(aContent);
   }
 
   MOZ_CRASH("Unkown pseudo-element given to "
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index b9778d36de..866fa148bf 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -1832,11 +1832,7 @@ nsCSSFrameConstructor::CreateGeneratedContentItem(nsFrameConstructorState& aStat
              aPseudoElement == CSSPseudoElementType::after,
              "unexpected aPseudoElement");
 
-  // XXXbz is this ever true?
-  if (!aParentContent->IsElement()) {
-    NS_ERROR("Bogus generated content parent");
-    return;
-  }
+  MOZ_ASSERT(aParentContent->IsElement());
 
   StyleSetHandle styleSet = mPresShell->StyleSet();
 
@@ -1864,6 +1860,13 @@ nsCSSFrameConstructor::CreateGeneratedContentItem(nsFrameConstructorState& aStat
   nsresult rv = NS_NewXMLElement(getter_AddRefs(container), nodeInfo.forget());
   if (NS_FAILED(rv))
     return;
+
+  // Cleared when the pseudo is unbound from the tree, so no need to store a
+  // strong reference, nor a destructor.
+  nsIAtom* property = isBefore
+    ? nsGkAtoms::beforePseudoProperty : nsGkAtoms::afterPseudoProperty;
+  aParentContent->SetProperty(property, container.get());
+
   container->SetIsNativeAnonymousRoot();
   container->SetPseudoElementType(aPseudoElement);
 
@@ -6079,6 +6082,9 @@ AddGenConPseudoToFrame(nsIFrame* aOwnerFrame, nsIContent* aContent)
   NS_ASSERTION(nsLayoutUtils::IsFirstContinuationOrIBSplitSibling(aOwnerFrame),
                "property should only be set on first continuation/ib-sibling");
 
+  // FIXME(emilio): Remove this property, and use the frame of the generated
+  // content itself to tear the content down? It should be quite simpler.
+
   nsIFrame::ContentArray* value =
     aOwnerFrame->GetProperty(nsIFrame::GenConProperty());
   if (!value) {
@@ -6340,7 +6346,7 @@ AdjustAppendParentForAfterContent(nsFrameManager* aFrameManager,
   // frames to find the first one that is either a ::after frame for an
   // ancestor of aChild or a frame that is for a node later in the
   // document than aChild and return that in aAfterFrame.
-  if (aParentFrame->GetGenConPseudos() ||
+  if (aParentFrame->GetProperty(nsIFrame::GenConProperty()) ||
       nsLayoutUtils::HasPseudoStyle(aContainer, aParentFrame->StyleContext(),
                                     CSSPseudoElementType::after,
                                     aParentFrame->PresContext()) ||
@@ -6669,9 +6675,8 @@ nsCSSFrameConstructor::FindFrameForContentSibling(nsIContent* aContent,
   nsIFrame* sibling = aContent->GetPrimaryFrame();
   if (!sibling && GetDisplayContentsStyleFor(aContent)) {
     // A display:contents node - check if it has a ::before / ::after frame...
-    sibling = aPrevSibling ?
-      nsLayoutUtils::GetAfterFrameForContent(aParentFrame, aContent) :
-      nsLayoutUtils::GetBeforeFrameForContent(aParentFrame, aContent);
+    sibling = aPrevSibling ? nsLayoutUtils::GetAfterFrame(aContent)
+                           : nsLayoutUtils::GetBeforeFrame(aContent);
     if (!sibling) {
       // ... then recurse into children ...
       const bool forward = !aPrevSibling;
@@ -6682,9 +6687,8 @@ nsCSSFrameConstructor::FindFrameForContentSibling(nsIContent* aContent,
     }
     if (!sibling) {
       // ... then ::after / ::before on the opposite end.
-      sibling = aPrevSibling ?
-        nsLayoutUtils::GetBeforeFrameForContent(aParentFrame, aContent) :
-        nsLayoutUtils::GetAfterFrameForContent(aParentFrame, aContent);
+      sibling = aPrevSibling ? nsLayoutUtils::GetAfterFrame(aContent)
+                             : nsLayoutUtils::GetBeforeFrame(aContent);
     }
     if (!sibling) {
       return nullptr;
@@ -8291,26 +8295,23 @@ nsCSSFrameConstructor::ContentRemoved(nsIContent*  aContainer,
   MOZ_ASSERT(!childFrame || !GetDisplayContentsStyleFor(aChild),
              "display:contents nodes shouldn't have a frame");
   if (!childFrame && GetDisplayContentsStyleFor(aChild)) {
-    nsIFrame* ancestorFrame = nullptr;
     nsIContent* ancestor = aContainer;
-    for (; ancestor; ancestor = ancestor->GetParent()) {
-      ancestorFrame = ancestor->GetPrimaryFrame();
-      if (ancestorFrame) {
-        break;
-      }
+    while (!ancestor->GetPrimaryFrame()) {
+      // FIXME(emilio): Should this use the flattened tree parent instead?
+      ancestor = ancestor->GetParent();
+      MOZ_ASSERT(ancestor, "we can't have a display: contents subtree root!");
     }
-    if (ancestorFrame) {
-      nsIFrame* contentInsertion = ancestorFrame->GetContentInsertionFrame();
-      if (ancestorFrame->GetGenConPseudos() ||
-          (contentInsertion && contentInsertion->GetGenConPseudos())) {
-        *aDidReconstruct = true;
-        LAYOUT_PHASE_TEMP_EXIT();
-        // XXXmats Can we recreate frames only for the ::after/::before content?
-        // XXX Perhaps even only those that belong to the aChild sub-tree?
-        RecreateFramesForContent(ancestor, false, aFlags, aDestroyedFramesFor);
-        LAYOUT_PHASE_TEMP_REENTER();
-        return;
-      }
+
+    nsIFrame* ancestorFrame = ancestor->GetPrimaryFrame();
+    if (ancestorFrame->GetProperty(nsIFrame::GenConProperty())) {
+      *aDidReconstruct = true;
+      LAYOUT_PHASE_TEMP_EXIT();
+
+      // XXXmats Can we recreate frames only for the ::after/::before content?
+      // XXX Perhaps even only those that belong to the aChild sub-tree?
+      RecreateFramesForContent(ancestor, false, aFlags, aDestroyedFramesFor);
+      LAYOUT_PHASE_TEMP_REENTER();
+      return;
     }
 
     FlattenedChildIterator iter(aChild);
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 21d20c69fa..de34822460 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1486,90 +1486,38 @@ nsLayoutUtils::GetChildListNameFor(nsIFrame* aChildFrame)
   return id;
 }
 
-/*static*/ nsIFrame*
-nsLayoutUtils::GetBeforeFrameForContent(nsIFrame* aFrame,
-                                        const nsIContent* aContent)
-{
-  // We need to call GetGenConPseudos() on the first continuation/ib-split.
-  // Find it, for symmetry with GetAfterFrameForContent.
-  nsContainerFrame* genConParentFrame =
-    FirstContinuationOrIBSplitSibling(aFrame)->GetContentInsertionFrame();
-  if (!genConParentFrame) {
-    return nullptr;
-  }
-  nsTArray<nsIContent*>* prop = genConParentFrame->GetGenConPseudos();
-  if (prop) {
-    const nsTArray<nsIContent*>& pseudos(*prop);
-    for (uint32_t i = 0; i < pseudos.Length(); ++i) {
-      if (pseudos[i]->GetParent() == aContent &&
-          pseudos[i]->NodeInfo()->NameAtom() == nsGkAtoms::mozgeneratedcontentbefore) {
-        return pseudos[i]->GetPrimaryFrame();
-      }
-    }
-  }
-  // If the first child frame is a pseudo-frame, then try that.
-  // Note that the frame we create for the generated content is also a
-  // pseudo-frame and so don't drill down in that case.
-  nsIFrame* childFrame = genConParentFrame->PrincipalChildList().FirstChild();
-  if (childFrame &&
-      childFrame->IsPseudoFrame(aContent) &&
-      !childFrame->IsGeneratedContentFrame()) {
-    return GetBeforeFrameForContent(childFrame, aContent);
-  }
-  return nullptr;
+static Element*
+GetPseudo(const nsIContent* aContent, nsIAtom* aPseudoProperty)
+{
+  MOZ_ASSERT(aPseudoProperty == nsGkAtoms::beforePseudoProperty ||
+             aPseudoProperty == nsGkAtoms::afterPseudoProperty);
+  return static_cast<Element*>(aContent->GetProperty(aPseudoProperty));
 }
 
-/*static*/ nsIFrame*
-nsLayoutUtils::GetBeforeFrame(nsIFrame* aFrame)
+/*static*/ Element*
+nsLayoutUtils::GetBeforePseudo(const nsIContent* aContent)
 {
-  return GetBeforeFrameForContent(aFrame, aFrame->GetContent());
+  return GetPseudo(aContent, nsGkAtoms::beforePseudoProperty);
 }
 
 /*static*/ nsIFrame*
-nsLayoutUtils::GetAfterFrameForContent(nsIFrame* aFrame,
-                                       const nsIContent* aContent)
-{
-  // We need to call GetGenConPseudos() on the first continuation,
-  // but callers are likely to pass the last.
-  nsContainerFrame* genConParentFrame =
-    FirstContinuationOrIBSplitSibling(aFrame)->GetContentInsertionFrame();
-  if (!genConParentFrame) {
-    return nullptr;
-  }
-  nsTArray<nsIContent*>* prop = genConParentFrame->GetGenConPseudos();
-  if (prop) {
-    const nsTArray<nsIContent*>& pseudos(*prop);
-    for (uint32_t i = 0; i < pseudos.Length(); ++i) {
-      if (pseudos[i]->GetParent() == aContent &&
-          pseudos[i]->NodeInfo()->NameAtom() == nsGkAtoms::mozgeneratedcontentafter) {
-        return pseudos[i]->GetPrimaryFrame();
-      }
-    }
-  }
-  // If the last child frame is a pseudo-frame, then try that.
-  // Note that the frame we create for the generated content is also a
-  // pseudo-frame and so don't drill down in that case.
-  genConParentFrame = aFrame->GetContentInsertionFrame();
-  if (!genConParentFrame) {
-    return nullptr;
-  }
-  nsIFrame* lastParentContinuation =
-    LastContinuationWithChild(static_cast<nsContainerFrame*>(
-      LastContinuationOrIBSplitSibling(genConParentFrame)));
-  nsIFrame* childFrame =
-    lastParentContinuation->GetChildList(nsIFrame::kPrincipalList).LastChild();
-  if (childFrame &&
-      childFrame->IsPseudoFrame(aContent) &&
-      !childFrame->IsGeneratedContentFrame()) {
-    return GetAfterFrameForContent(childFrame->FirstContinuation(), aContent);
-  }
-  return nullptr;
+nsLayoutUtils::GetBeforeFrame(const nsIContent* aContent)
+{
+  Element* pseudo = GetBeforePseudo(aContent);
+  return pseudo ? pseudo->GetPrimaryFrame() : nullptr;
+}
+
+/*static*/ Element*
+nsLayoutUtils::GetAfterPseudo(const nsIContent* aContent)
+{
+  return GetPseudo(aContent, nsGkAtoms::afterPseudoProperty);
 }
 
 /*static*/ nsIFrame*
-nsLayoutUtils::GetAfterFrame(nsIFrame* aFrame)
+nsLayoutUtils::GetAfterFrame(const nsIContent* aContent)
 {
-  return GetAfterFrameForContent(aFrame, aFrame->GetContent());
+  Element* pseudo = GetAfterPseudo(aContent);
+  return pseudo ? pseudo->GetPrimaryFrame() : nullptr;
 }
 
 // static
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index bba1f32652..9757cb7999 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -276,50 +276,26 @@ public:
   static mozilla::layout::FrameChildListID GetChildListNameFor(nsIFrame* aChildFrame);
 
   /**
-   * GetBeforeFrameForContent returns the ::before frame for aContent, if
-   * one exists.  This is typically O(1).  The frame passed in must be
-   * the first-in-flow.
-   *
-   * @param aGenConParentFrame an ancestor of the ::before frame
-   * @param aContent the content whose ::before is wanted
-   * @return the ::before frame or nullptr if there isn't one
+   * Returns the ::before pseudo-element for aContent, if any.
    */
-  static nsIFrame* GetBeforeFrameForContent(nsIFrame* aGenConParentFrame,
-                                            const nsIContent* aContent);
+  static mozilla::dom::Element* GetBeforePseudo(const nsIContent* aContent);
 
   /**
-   * GetBeforeFrame returns the outermost ::before frame of the given frame, if
-   * one exists.  This is typically O(1).  The frame passed in must be
-   * the first-in-flow.
-   *
-   * @param aFrame the frame whose ::before is wanted
-   * @return the :before frame or nullptr if there isn't one
+   * Returns the frame corresponding to the ::before pseudo-element for
+   * aContent, if any.
    */
-  static nsIFrame* GetBeforeFrame(nsIFrame* aFrame);
+  static nsIFrame* GetBeforeFrame(const nsIContent* aContent);
 
   /**
-   * GetAfterFrameForContent returns the ::after frame for aContent, if one
-   * exists.  This will walk the in-flow chain of aGenConParentFrame to the
-   * last-in-flow if needed.  This function is typically O(N) in the number
-   * of child frames, following in-flows, etc.
-   *
-   * @param aGenConParentFrame an ancestor of the ::after frame
-   * @param aContent the content whose ::after is wanted
-   * @return the ::after frame or nullptr if there isn't one
+   * Returns the ::after pseudo-element for aContent, if any.
    */
-  static nsIFrame* GetAfterFrameForContent(nsIFrame* aGenConParentFrame,
-                                           const nsIContent* aContent);
+  static mozilla::dom::Element* GetAfterPseudo(const nsIContent* aContent);
 
   /**
-   * GetAfterFrame returns the outermost ::after frame of the given frame, if one
-   * exists.  This will walk the in-flow chain to the last-in-flow if
-   * needed.  This function is typically O(N) in the number of child
-   * frames, following in-flows, etc.
-   *
-   * @param aFrame the frame whose ::after is wanted
-   * @return the :after frame or nullptr if there isn't one
+   * Returns the frame corresponding to the ::after pseudo-element for aContent,
+   * if any.
    */
-  static nsIFrame* GetAfterFrame(nsIFrame* aFrame);
+  static nsIFrame* GetAfterFrame(const nsIContent* aContent);
 
   /**
    * Given a frame, search up the frame tree until we find an
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 71f6172bd5..25b685fb28 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -10008,19 +10008,16 @@ nsIFrame::IsPseudoStackingContextFromStyle() {
 Element*
 nsIFrame::GetPseudoElement(CSSPseudoElementType aType)
 {
-  nsIFrame* frame = nullptr;
+  if (!mContent) {
+    return nullptr;
+  }
 
   if (aType == CSSPseudoElementType::before) {
-    frame = nsLayoutUtils::GetBeforeFrame(this);
-  } else if (aType == CSSPseudoElementType::after) {
-    frame = nsLayoutUtils::GetAfterFrame(this);
+    return nsLayoutUtils::GetBeforePseudo(mContent);
   }
 
-  if (frame) {
-    nsIContent* content = frame->GetContent();
-    if (content->IsElement()) {
-      return content->AsElement();
-    }
+  if (aType == CSSPseudoElementType::after) {
+    return nsLayoutUtils::GetAfterPseudo(mContent);
   }
 
   return nullptr;
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 3137aaee27..9372b15a2a 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -1062,10 +1062,6 @@ public:
     return GetBidiData().embeddingLevel;
   }
 
-  nsTArray<nsIContent*>* GetGenConPseudos() {
-    return GetProperty(GenConProperty());
-  }
-
   /**
    * Return the distance between the border edge of the frame and the
    * margin edge of the frame.  Like GetRect(), returns the dimensions
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 102e0df18c..20e5651bd4 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -638,6 +638,34 @@ nsComputedDOMStyle::SetFrameStyleContext(nsStyleContext* aContext)
   mStyleContext = aContext;
 }
 
+/**
+ * The following function checks whether we need to explicitly resolve the style
+ * again, even though we have a style context coming from the frame.
+ *
+ * This basically checks whether the style is or may be under a ::first-line or
+ * ::first-letter frame, in which case we can't return the frame style, and we
+ * need to resolve it. See bug 505515.
+ */
+static bool
+MustReresolveStyle(const nsStyleContext* aContext)
+{
+  MOZ_ASSERT(aContext);
+
+  if (aContext->HasPseudoElementData()) {
+    if (!aContext->GetPseudo() ||
+        aContext->StyleSource().IsServoComputedValues()) {
+      // TODO(emilio): When ::first-line is supported in Servo, we may want to
+      // fix this to avoid re-resolving pseudo-element styles.
+      return true;
+    }
+
+    return aContext->GetParent() &&
+           aContext->GetParent()->HasPseudoElementData();
+  }
+
+  return false;
+}
+
 void
 nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
 {
@@ -690,9 +718,20 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
   // XXX the !mElement->IsHTMLElement(nsGkAtoms::area)
   // check is needed due to bug 135040 (to avoid using
   // mPrimaryFrame). Remove it once that's fixed.
-  if (!mPseudo && mStyleType == eAll &&
-      !mElement->IsHTMLElement(nsGkAtoms::area)) {
-    mOuterFrame = mElement->GetPrimaryFrame();
+  if (mStyleType == eAll && !mElement->IsHTMLElement(nsGkAtoms::area)) {
+    mOuterFrame = nullptr;
+
+    if (!mPseudo) {
+      mOuterFrame = mElement->GetPrimaryFrame();
+    } else if (mPseudo == nsCSSPseudoElements::before ||
+               mPseudo == nsCSSPseudoElements::after) {
+      nsIAtom* property = mPseudo == nsCSSPseudoElements::before
+                            ? nsGkAtoms::beforePseudoProperty
+                            : nsGkAtoms::afterPseudoProperty;
+
+      auto* pseudo = static_cast<Element*>(mElement->GetProperty(property));
+      mOuterFrame = pseudo ? pseudo->GetPrimaryFrame() : nullptr;
+    }
     mInnerFrame = mOuterFrame;
     if (mOuterFrame) {
       nsIAtom* type = mOuterFrame->GetType();
@@ -711,7 +750,7 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
     }
   }
 
-  if (!mStyleContext || mStyleContext->HasPseudoElementData()) {
+  if (!mStyleContext || MustReresolveStyle(mStyleContext)) {
 #ifdef DEBUG
     if (mStyleContext) {
       // We want to check that going through this path because of