3 files changed, 20 insertions, 7 deletions
diff --git a/layout/style/res/forms.css b/layout/style/res/forms.css
index 95025221d1..c91c2f7392 100644
--- a/layout/style/res/forms.css
+++ b/layout/style/res/forms.css
@@ -1099,6 +1099,7 @@ input[type=number]::-moz-number-spin-box {
 }
 
 input[type=number]::-moz-number-spin-up {
+  writing-mode: horizontal-tb;
   -moz-appearance: spinner-upbutton;
   display: block; /* bug 926670 */
   flex: none;
@@ -1116,6 +1117,7 @@ input[type=number]::-moz-number-spin-up {
 }
 
 input[type=number]::-moz-number-spin-down {
+  writing-mode: horizontal-tb;
   -moz-appearance: spinner-downbutton;
   display: block; /* bug 926670 */
   flex: none;
diff --git a/layout/style/res/html.css b/layout/style/res/html.css
index 1f572467f3..ea8efbe24d 100644
--- a/layout/style/res/html.css
+++ b/layout/style/res/html.css
@@ -7,18 +7,18 @@
 
 /* bidi */
 
-[dir] {
+:-moz-has-dir-attr {
   unicode-bidi: isolate;
 }
-[dir="rtl"] {
+:-moz-dir-attr-rtl {
   direction: rtl;
 }
-[dir="ltr"] {
+:-moz-dir-attr-ltr {
   direction: ltr;
 }
 
-bdi:dir(ltr), [dir="auto"]:dir(ltr) { direction: ltr; }
-bdi:dir(rtl), [dir="auto"]:dir(rtl) { direction: rtl; }
+:-moz-dir-attr-like-auto:dir(ltr) { direction: ltr; }
+:-moz-dir-attr-like-auto:dir(rtl) { direction: rtl; }
 
 /* To ensure http://www.w3.org/TR/REC-html40/struct/dirlang.html#style-bidi:
  *
@@ -89,10 +89,15 @@ xmp {
 bdi, output {
   unicode-bidi: isolate;
 }
-bdo, bdo[dir] {
+/* We need the "bdo:-moz-has-dir-attr" bit because "bdo" has lower
+   specificity than the ":-moz-has-dir-attr" selector above. */
+bdo, bdo:-moz-has-dir-attr {
   unicode-bidi: isolate-override;
 }
-textarea[dir="auto"], pre[dir="auto"] { unicode-bidi: plaintext; }
+textarea:-moz-dir-attr-like-auto,
+pre:-moz-dir-attr-like-auto {
+    unicode-bidi: plaintext;
+}
 
 /* blocks */
 
diff --git a/layout/style/res/ua.css b/layout/style/res/ua.css
index 931b32eb86..504f5dc570 100644
--- a/layout/style/res/ua.css
+++ b/layout/style/res/ua.css
@@ -471,3 +471,9 @@ div:-moz-native-anonymous.moz-custom-content-container {
   width: 100%;
   height: 100%;
 }
+
+/* Shadow DOM v1
+ * https://drafts.csswg.org/css-scoping/#slots-in-shadow-tree */
+slot {
+  display: contents;
+}
+\ No newline at end of file