At the moment, the NS_RunnableMethod family produces a Runnable that releases its reference to the object upon destruction. However, there is no guarantee when the Runnable is destroyed and on which thread. Therefore, this is not compatible with nsMainThreadPtrHandle. We should provide a specialization of the NS_RunnableMethod family that makes sure we release nsMainThreadPtrHandle on the main thread. Note that the main thread may be either the calling thread or the dispatch target.

I don't think this a problem; nsMainThreadPtrHandle holds an nsMainThreadPtrHolder, which in turn ensures whatever it's holding on to is released on the main thread whenever nsMainThreadPtrHolder is destroyed. Please correct me if I'm misunderstanding the problem here.