All proposed solutions in the forum thread are either unsafe or doesn't keep the desired functionality.
It is unsafe to access ANY property of wrappedJSObject. An attack is based on a malformed getter on a prototype property.
Theoretically there is yet watch-based attack. But it seems like Firefox (tested on FF 3.6) does not call watcher on indirect property assignment (through attribute assignment). To be more safe the setAttribute called on the wrapper.
See jquery-1.4.2.js.GMfix.diff patch.