diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 078cbaecdf..4be2372347 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -4667,7 +4667,7 @@ CSSParserImpl::ParseSupportsConditionInParens(bool& aConditionMet)
     return true;
   }
 
-  if (AgentRulesEnabled() &&
+  if ((AgentRulesEnabled() || ChromeRulesEnabled()) &&
       mToken.mType == eCSSToken_Function &&
       mToken.mIdent.LowerCaseEqualsLiteral("-moz-bool-pref")) {
     return ParseSupportsMozBoolPrefName(aConditionMet);