--- a/layout/style/Rule.h
+++ b/layout/style/Rule.h
@@ -113,17 +113,17 @@ public:
   // This is pure virtual because all of Rule's data members are non-owning and
   // thus measured elsewhere.
   virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
     const MOZ_MUST_OVERRIDE = 0;
 
   // WebIDL interface, aka helpers for nsIDOMCSSRule implementation.
   virtual uint16_t Type() const = 0;
   virtual void GetCssTextImpl(nsAString& aCssText) const = 0;
-  // XPCOM GetCssText is OK, since it never throws.
+  void GetCssText(nsAString& aCssText) const { GetCssTextImpl(aCssText); }
   // XPCOM SetCssText is OK, since it never throws.
   Rule* GetParentRule() const;
   StyleSheet* GetParentStyleSheet() const { return GetStyleSheet(); }
   nsIDocument* GetParentObject() const { return GetDocument(); }
 
 protected:
   // True if we're known-live for cycle collection purposes.
   bool IsKnownLive() const;