--- a/editor/libeditor/HTMLEditor.cpp
+++ b/editor/libeditor/HTMLEditor.cpp
@@ -4395,17 +4395,17 @@ HTMLEditor::RemoveAttributeOrEquivalent(
     return NS_OK;
   }
 
   return aSuppressTransaction ?
     aElement->UnsetAttr(kNameSpaceID_None, aAttribute, /* aNotify = */ true) :
     RemoveAttributeWithTransaction(*aElement, *aAttribute);
 }
 
-nsresult
+NS_IMETHODIMP
 HTMLEditor::SetIsCSSEnabled(bool aIsCSSPrefChecked)
 {
   if (!mCSSEditUtils) {
     return NS_ERROR_NOT_INITIALIZED;
   }
 
   mCSSEditUtils->SetCSSEnabled(aIsCSSPrefChecked);