It has been a while since I looked at this, so I don't quite recall which marking path is involved here, but it looks like the GC heap dumping is not recording the key: 0x4393c020 B WeakMap 46ebffd0 > 0x4391a6a0 B type > 0x43932c10 B shape > 0x474d69d0 B WeakMap entry > 0x47469040 B WeakMap entry > 0x4770d9a0 G WeakMap entry > 0x47766b50 G WeakMap entry > 0x47481b80 B WeakMap entry B2G seems to use many weak maps, so this could become important. I'm not sure the best way to fix this. The easiest short term fix may be for me to finally finish bug 692226 to add these to the CC log, then with an AllTraces log you could look up the keys in the CC log.

I think it should be easy to fix this. We need to set dtrc.eagerlyTraceWeakMaps = TraceWeakMapKeysValues in DumpHeapComplete right after initializing the tracer.

I was waiting for a build so I figured I'd whip this up.