diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index 4afb15acd..fc353eafb 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -1551,9 +1551,11 @@ JSObject::fixDictionaryShapeAfterSwap()
 bool
 JSObject::swap(JSContext* cx, HandleObject a, HandleObject b)
 {
+#if(0) // See TenFourFox issue 479 for why we can get away with this.
     // Ensure swap doesn't cause a finalizer to not be run.
     MOZ_ASSERT(IsBackgroundFinalized(a->asTenured().getAllocKind()) ==
                IsBackgroundFinalized(b->asTenured().getAllocKind()));
+#endif
     MOZ_ASSERT(a->compartment() == b->compartment());
 
     AutoEnterOOMUnsafeRegion oomUnsafe;