--- a/dom/xul/XULDocument.cpp
+++ b/dom/xul/XULDocument.cpp
@@ -2155,16 +2155,20 @@ XULDocument::ApplyPersistentAttributesTo
 
 void
 XULDocument::TraceProtos(JSTracer* aTrc, uint32_t aGCNumber)
 {
     uint32_t i, count = mPrototypes.Length();
     for (i = 0; i < count; ++i) {
         mPrototypes[i]->TraceProtos(aTrc, aGCNumber);
     }
+
+    if (mCurrentPrototype) {
+        mCurrentPrototype->TraceProtos(aTrc, aGCNumber);
+    }
 }
 
 //----------------------------------------------------------------------
 //
 // XULDocument::ContextStack
 //
 
 XULDocument::ContextStack::ContextStack()