When I run mochitest on my local (ubuntu) with debug enabled, I found some leaks from test_NestedFrames.html ./mach mochitest --keep-open=false dom/browser-element/mochitest/priority/test_NestedFrames.html == BloatView: ALL (cumulative) LEAK AND BLOAT STATISTICS, tab process 19777 |<----------------Class--------------->|<-----Bytes------>|<----Objects---->| | | Per-Inst Leaked| Total Rem| 0 |TOTAL | 41 4384| 56443 36| 9 |AsyncTransactionTrackersHolder | 72 72| 3 1| 43 |CompositorChild | 840 840| 1 1| 45 |CondVar | 40 120| 32 3| 137 |MessagePump | 16 16| 16 1| 139 |Mutex | 32 96| 102 3| 150 |PCompositorChild | 736 736| 1 1| 155 |PImageBridgeChild | 760 760| 1 1| 193 |RefCountedMonitor | 80 160| 5 2| 194 |RefCountedTask | 16 64| 10 4| 221 |StoreRef | 16 64| 6 4| 253 |WaitableEventKernel | 72 72| 19 1| 258 |WeakReference<MessageListener> | 16 32| 27 2| 306 |ipc::MessageChannel | 512 1024| 5 2| 586 |nsTArray_base | 8 72| 11520 9| 589 |nsThread | 256 256| 15 1| nsTraceRefcnt::DumpStatistics: 642 entries TEST-INFO | leakcheck | tab process: leaked 1 AsyncTransactionTrackersHolder (72 bytes) TEST-INFO | leakcheck | tab process: leaked 1 CompositorChild (840 bytes) TEST-INFO | leakcheck | tab process: leaked 3 CondVar (120 bytes) TEST-INFO | leakcheck | tab process: leaked 1 MessagePump (16 bytes) TEST-INFO | leakcheck | tab process: leaked 3 Mutex (96 bytes) TEST-INFO | leakcheck | tab process: leaked 1 PCompositorChild (736 bytes) TEST-INFO | leakcheck | tab process: leaked 1 PImageBridgeChild (760 bytes) TEST-INFO | leakcheck | tab process: leaked 2 RefCountedMonitor (160 bytes) TEST-INFO | leakcheck | tab process: leaked 4 RefCountedTask (64 bytes) TEST-INFO | leakcheck | tab process: leaked 4 StoreRef (64 bytes) TEST-INFO | leakcheck | tab process: leaked 1 WaitableEventKernel (72 bytes) TEST-INFO | leakcheck | tab process: leaked 2 WeakReference<MessageListener> (32 bytes) TEST-INFO | leakcheck | tab process: leaked 2 ipc::MessageChannel (1024 bytes) TEST-INFO | leakcheck | tab process: leaked 9 nsTArray_base (72 bytes) TEST-INFO | leakcheck | tab process: leaked 1 nsThread (256 bytes) WARNING | leakcheck | tab process: 4384 bytes leaked (AsyncTransactionTrackersHolder, CompositorChild, CondVar, MessagePump, Mutex, ...) == BloatView: ALL (cumulative) LEAK AND BLOAT STATISTICS, default process 19704 |<----------------Class--------------->|<-----Bytes------>|<----Objects---->| | | Per-Inst Leaked| Total Rem| 0 |TOTAL | 32 0| 1077847 0| nsTraceRefcnt::DumpStatistics: 1300 entries TEST-PASS | leakcheck | default process: no leaks detected! runtests.py | Running tests: end. 0 INFO TEST-START | Shutdown 1 INFO Passed: 4 2 INFO Failed: 0 3 INFO Todo: 0 4 INFO SimpleTest FINISHED SUITE-END | took 9s

I think I've see that leak randomly with random tests, so possibly not about test_NestedFrames.html (but if test_NestedFrames.html can be used to reproduce the leak reliably, great.)

Unfortunately, we actually always leak those objects when you have a tab process (in other words, a content process). The primary problem is that a few graphics-related IPDL actors (ImageBridgeChild and CompositorChild) aren't shut down properly. I'll dupe this to one of the existing bugs on those leaks.