--- a/layout/style/GroupRule.cpp
+++ b/layout/style/GroupRule.cpp
@@ -27,17 +27,17 @@ namespace css {
 // Style Rule List for group rules
 //
 
 class GroupRuleRuleList final : public dom::CSSRuleList
 {
 public:
   explicit GroupRuleRuleList(GroupRule *aGroupRule);
 
-  virtual CSSStyleSheet* GetParentObject() override;
+  StyleSheet* GetParentObject() override;
 
   virtual Rule*
   IndexedGetter(uint32_t aIndex, bool& aFound) override;
   virtual uint32_t
   Length() override;
 
   void DropReference() { mGroupRule = nullptr; }
 
@@ -54,24 +54,23 @@ GroupRuleRuleList::GroupRuleRuleList(Gro
   // The rule will tell us when its going away.
   mGroupRule = aGroupRule;
 }
 
 GroupRuleRuleList::~GroupRuleRuleList()
 {
 }
 
-CSSStyleSheet*
+StyleSheet*
 GroupRuleRuleList::GetParentObject()
 {
   if (!mGroupRule) {
     return nullptr;
   }
-  StyleSheet* sheet = mGroupRule->GetStyleSheet();
-  return sheet ? sheet->AsGecko() : nullptr;
+  return mGroupRule->GetStyleSheet();
 }
 
 uint32_t
 GroupRuleRuleList::Length()
 {
   if (!mGroupRule) {
     return 0;
   }