With the fix from bug 1637377 applied I now see a new hang. It takes a bit longer to reproduce but usually under a minute running the 'no-op' adapter in Grizzly.

Crash|SIGABRT|0x3e8000017b5|0
0|0|libpthread.so.0|__lll_lock_wait|||0x1d
0|1|libpthread.so.0|__pthread_mutex_lock|/build/glibc-LK5gWL/glibc-2.23/nptl/../nptl/pthread_mutex_lock.c|135|0x27
0|2|firefox-bin|arena_t::MallocSmall(unsigned long, bool)|hg:hg.mozilla.org/try:memory/build/mozjemalloc.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|2846|0xc
0|3|firefox-bin|Allocator<MozJemallocBase>::malloc(unsigned long)|hg:hg.mozilla.org/try:memory/build/malloc_decls.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|51|0x1eb
0|4|firefox-bin|replace_malloc|hg:hg.mozilla.org/try:memory/replace/phc/PHC.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|1122|0x18
0|5|firefox-bin|malloc|hg:hg.mozilla.org/try:memory/build/malloc_decls.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|51|0x2f
0|6|libxul.so|gcov_do_dump|/builds/worker/fetches/gcc-source/libgcc/libgcov-driver.c|843|0x50
0|7|libxul.so|__gcov_dump_one|/builds/worker/fetches/gcc-source/libgcc/libgcov-driver.c|871|0xe
0|8|libxul.so|__gcov_dump_int|/builds/worker/fetches/gcc-source/libgcc/libgcov-interface.c|164|0x8
0|9|libxul.so|__gcov_flush|/builds/worker/fetches/gcc-source/libgcc/libgcov-interface.c|88|0x5
0|10|libxul.so|mozilla::CodeCoverageHandler::FlushCounters()|hg:hg.mozilla.org/try:tools/code-coverage/CodeCoverageHandler.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|49|0x5
0|11|libxul.so|mozilla::CodeCoverageHandler::FlushCountersSignalHandler(int)|hg:hg.mozilla.org/try:tools/code-coverage/CodeCoverageHandler.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|97|0x12
0|12|libc.so.6||||0x354b0
0|13|firefox-bin|arena_t::MallocSmall(unsigned long, bool)|hg:hg.mozilla.org/try:memory/build/mozjemalloc.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|2849|0xb
0|14|firefox-bin|Allocator<MozJemallocBase>::malloc(unsigned long)|hg:hg.mozilla.org/try:memory/build/malloc_decls.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|51|0x1eb
0|15|firefox-bin|replace_malloc|hg:hg.mozilla.org/try:memory/replace/phc/PHC.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|1122|0x18
0|16|firefox-bin|malloc|hg:hg.mozilla.org/try:memory/build/malloc_decls.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|51|0x2f
0|17|firefox-bin|moz_xmalloc|hg:hg.mozilla.org/try:memory/mozalloc/mozalloc.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|52|0x8
0|18|libxul.so|nsTArrayInfallibleAllocator::ResultTypeProxy nsTArray_base<nsTArrayInfallibleAllocator, nsTArray_RelocateUsingMoveConstructor<regiondetails::Band> >::EnsureCapacity<nsTArrayInfallibleAllocator>(unsigned long, unsigned long)|hg:hg.mozilla.org/try:xpcom/ds/nsTArray-inl.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|162|0x5
0|19|libxul.so|regiondetails::Band* nsTArray_Impl<regiondetails::Band, nsTArrayInfallibleAllocator>::ReplaceElementsAtInternal<nsTArrayInfallibleAllocator, regiondetails::Band>(unsigned long, unsigned long, regiondetails::Band const*, unsigned long)|hg:hg.mozilla.org/try:xpcom/ds/nsTArray.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|2322|0x1b
0|20|libxul.so|nsRegion::Copy(nsRegion const&)|hg:hg.mozilla.org/try:gfx/src/nsRegion.h:b50801947c0de6d0e88d932ba444ea3759e0e6b2|1907|0x1e
0|21|libxul.so|mozilla::layers::ShadowLayerForwarder::EndTransaction(mozilla::gfx::IntRegionTyped<mozilla::gfx::UnknownUnits> const&, mozilla::layers::BaseTransactionId<mozilla::layers::TransactionIdType>, bool, unsigned int, bool, mozilla::layers::BaseTransactionId<mozilla::VsyncIdType> const&, mozilla::TimeStamp const&, mozilla::TimeStamp const&, mozilla::TimeStamp const&, bool, nsTString<char> const&, bool*, nsTArray<mozilla::layers::CompositionPayload> const&)|hg:hg.mozilla.org/try:gfx/layers/ipc/ShadowLayers.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|619|0x29
0|22|libxul.so|mozilla::layers::ClientLayerManager::ForwardTransaction(bool)|hg:hg.mozilla.org/try:gfx/layers/client/ClientLayerManager.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|734|0x1e
0|23|libxul.so|mozilla::layers::ClientLayerManager::EndTransaction(void (*)(mozilla::layers::PaintedLayer*, gfxContext*, mozilla::gfx::IntRegionTyped<mozilla::gfx::UnknownUnits> const&, mozilla::gfx::IntRegionTyped<mozilla::gfx::UnknownUnits> const&, mozilla::layers::DrawRegionClip, mozilla::gfx::IntRegionTyped<mozilla::gfx::UnknownUnits> const&, void*), void*, mozilla::layers::LayerManager::EndTransactionFlags)|hg:hg.mozilla.org/try:gfx/layers/client/ClientLayerManager.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|409|0x12
0|24|libxul.so|nsDisplayList::PaintRoot(nsDisplayListBuilder*, gfxContext*, unsigned int)|hg:hg.mozilla.org/try:layout/painting/nsDisplayList.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|2484|0x13
0|25|libxul.so|nsLayoutUtils::PaintFrame(gfxContext*, nsIFrame*, nsRegion const&, unsigned int, nsDisplayListBuilderMode, nsLayoutUtils::PaintFrameFlags)|hg:hg.mozilla.org/try:layout/base/nsLayoutUtils.cpp:b50801947c0de6d0e88d932ba444ea3759e0e6b2|4141|0x19
0|26|libxul.so||||0x7973ff0
0|27|libxul.so|_fini|||0x41957f8

The severity field is not set for this bug.
:ekyle, could you have a look please?

For more information, please visit auto_nag documentation.

A lot has changed here and I am no longer seeing this.