diff --git a/mozilla/content/html/style/src/nsCSSParser.cpp b/mozilla/content/html/style/src/nsCSSParser.cpp
index c05413f1b83..c556da1383b 100644
--- a/mozilla/content/html/style/src/nsCSSParser.cpp
+++ b/mozilla/content/html/style/src/nsCSSParser.cpp
@@ -2207,11 +2207,13 @@ void CSSParserImpl::ParsePseudoSelector(PRInt32&  aDataMask,
       aParsingStatus = SELECTOR_PARSING_STOPPED_ERROR;
       return;
     }
-    // CSS2 pseudo-elements are allowed to have a single ':' on them.  Others
-    // (CSS3+ pseudo-elements and various -moz-* pseudo-elements) must have
-    // |parsingPseudoElement| set.
+    // CSS2 pseudo-elements and -moz-tree-* pseudo-elements are allowed
+    // to have a single ':' on them.  Others (CSS3+ pseudo-elements and
+    // various -moz-* pseudo-elements) must have |parsingPseudoElement|
+    // set.
     if (!parsingPseudoElement &&
-        !nsCSSPseudoElements::IsCSS2PseudoElement(pseudo)) {
+        !nsCSSPseudoElements::IsCSS2PseudoElement(pseudo) &&
+        !IsTreePseudoElement(pseudo)) {
       REPORT_UNEXPECTED_TOKEN(NS_LITERAL_STRING("This pseudo-element must use the \"::\" form: "));
       UngetToken();
       aParsingStatus = SELECTOR_PARSING_STOPPED_ERROR;
diff --git a/mozilla/layout/style/nsCSSParser.cpp b/mozilla/layout/style/nsCSSParser.cpp
index c05413f1b83..c556da1383b 100644
--- a/mozilla/layout/style/nsCSSParser.cpp
+++ b/mozilla/layout/style/nsCSSParser.cpp
@@ -2207,11 +2207,13 @@ void CSSParserImpl::ParsePseudoSelector(PRInt32&  aDataMask,
       aParsingStatus = SELECTOR_PARSING_STOPPED_ERROR;
       return;
     }
-    // CSS2 pseudo-elements are allowed to have a single ':' on them.  Others
-    // (CSS3+ pseudo-elements and various -moz-* pseudo-elements) must have
-    // |parsingPseudoElement| set.
+    // CSS2 pseudo-elements and -moz-tree-* pseudo-elements are allowed
+    // to have a single ':' on them.  Others (CSS3+ pseudo-elements and
+    // various -moz-* pseudo-elements) must have |parsingPseudoElement|
+    // set.
     if (!parsingPseudoElement &&
-        !nsCSSPseudoElements::IsCSS2PseudoElement(pseudo)) {
+        !nsCSSPseudoElements::IsCSS2PseudoElement(pseudo) &&
+        !IsTreePseudoElement(pseudo)) {
       REPORT_UNEXPECTED_TOKEN(NS_LITERAL_STRING("This pseudo-element must use the \"::\" form: "));
       UngetToken();
       aParsingStatus = SELECTOR_PARSING_STOPPED_ERROR;