Backed out changeset baa67a17c11e (Bug 1741995) for causing valgrind bustages.
Backout link
Push with failures
Failure Log
There are also assertion failures - Failure Log

Backed out for causing assertion failures on htmlparser/nsExpatDriver.cpp.

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=b7318976c3b9d207db6bd613de8b0e28c020934a&selectedTaskRun=O6YLP__FQxCjkp_uTu0erw.0

Failure logs: https://treeherder.mozilla.org/logviewer?job_id=359201967&repo=autoland
https://treeherder.mozilla.org/logviewer?job_id=359201731&repo=autoland

Backout link: https://hg.mozilla.org/integration/autoland/rev/4514714d7da638c66dce012e84948df84c5434d0

[task 2021-11-25T08:57:20.120Z] 08:57:20     INFO - GECKO(8684) | [Parent 7016, Main Thread] WARNING: '!inner', file /builds/worker/checkouts/gecko/dom/ipc/jsactor/JSWindowActorProtocol.cpp:184
[task 2021-11-25T08:57:20.121Z] 08:57:20     INFO - GECKO(8684) | [Parent 7016, Main Thread] WARNING: '!inner', file /builds/worker/checkouts/gecko/dom/ipc/jsactor/JSWindowActorProtocol.cpp:184
[task 2021-11-25T08:57:20.121Z] 08:57:20     INFO - GECKO(8684) | [Parent 7016, Main Thread] WARNING: '!inner', file /builds/worker/checkouts/gecko/dom/ipc/jsactor/JSWindowActorProtocol.cpp:184
[task 2021-11-25T08:57:20.122Z] 08:57:20     INFO - GECKO(8684) | [Parent 7016, Main Thread] ###!!! ASSERTION: Inconsistent expat suspension state.: 'status != XML_STATUS_SUSPENDED || BlockedOrInterrupted()', file /builds/worker/checkouts/gecko/parser/htmlparser/nsExpatDriver.cpp:1184
[task 2021-11-25T08:57:20.261Z] 08:57:20     INFO -  Initializing stack-fixing for the first stack frame, this may take a while...
[task 2021-11-25T08:57:30.651Z] 08:57:30     INFO - GECKO(8684) | #01: NS_DebugBreak(unsigned int, char const*, char const*, char const*, int) [xpcom/base/nsDebugImpl.cpp:429]
[task 2021-11-25T08:57:30.659Z] 08:57:30     INFO - GECKO(8684) | #02: nsExpatDriver::ParseBuffer(char16_t const*, unsigned int, bool, unsigned int*) [parser/htmlparser/nsExpatDriver.cpp:1183]
[task 2021-11-25T08:57:30.660Z] 08:57:30     INFO - GECKO(8684) | #03: nsExpatDriver::ConsumeToken(nsScanner&, bool&) [parser/htmlparser/nsExpatDriver.cpp:1262]
[task 2021-11-25T08:57:30.660Z] 08:57:30     INFO - GECKO(8684) | #04: nsParser::Tokenize(bool) [parser/htmlparser/nsParser.cpp:1392]
[task 2021-11-25T08:57:30.661Z] 08:57:30     INFO - GECKO(8684) | #05: nsParser::ResumeParse(bool, bool, bool) [parser/htmlparser/nsParser.cpp:954]
[task 2021-11-25T08:57:30.661Z] 08:57:30     INFO - GECKO(8684) | #06: nsParser::OnDataAvailable(nsIRequest*, nsIInputStream*, unsigned long long, unsigned int) [parser/htmlparser/nsParser.cpp:1306]
[task 2021-11-25T08:57:30.662Z] 08:57:30     INFO - GECKO(8684) | #07: mozilla::net::nsHttpChannel::OnDataAvailable(nsIRequest*, nsIInputStream*, unsigned long long, unsigned int) [netwerk/protocol/http/nsHttpChannel.cpp:7683]
[task 2021-11-25T08:57:30.662Z] 08:57:30     INFO - GECKO(8684) | #08: nsInputStreamPump::OnStateTransfer() [netwerk/base/nsInputStreamPump.cpp:532]
[task 2021-11-25T08:57:30.663Z] 08:57:30     INFO - GECKO(8684) | #09: nsInputStreamPump::OnInputStreamReady(nsIAsyncInputStream*) [netwerk/base/nsInputStreamPump.cpp:389]
[task 2021-11-25T08:57:30.663Z] 08:57:30     INFO - GECKO(8684) | #10: nsInputStreamReadyEvent::Run() [xpcom/io/nsStreamUtils.cpp:96]
[task 2021-11-25T08:57:30.664Z] 08:57:30     INFO - GECKO(8684) | #11: mozilla::RunnableTask::Run() [xpcom/threads/TaskController.cpp:469]
[task 2021-11-25T08:57:30.664Z] 08:57:30     INFO - GECKO(8684) | #12: mozilla::TaskController::DoExecuteNextTaskOnlyMainThreadInternal(mozilla::detail::BaseAutoLock<mozilla::Mutex &> const&) [xpcom/threads/TaskController.cpp:771]
[task 2021-11-25T08:57:30.665Z] 08:57:30     INFO - GECKO(8684) | #13: mozilla::TaskController::ExecuteNextTaskOnlyMainThreadInternal(mozilla::detail::BaseAutoLock<mozilla::Mutex &> const&) [xpcom/threads/TaskController.cpp:607]
[task 2021-11-25T08:57:30.665Z] 08:57:30     INFO - GECKO(8684) | #14: mozilla::TaskController::ProcessPendingMTTask(bool) [xpcom/threads/TaskController.cpp:391]
[task 2021-11-25T08:57:30.666Z] 08:57:30     INFO - GECKO(8684) | #15: mozilla::detail::RunnableFunction<`lambda at /builds/worker/checkouts/gecko/xpcom/threads/TaskController.cpp:124:7'>::Run() [xpcom/threads/nsThreadUtils.h:532]
[task 2021-11-25T08:57:30.667Z] 08:57:30     INFO - GECKO(8684) | #16: nsThread::ProcessNextEvent(bool, bool*) [xpcom/threads/nsThread.cpp:1187]
[task 2021-11-25T08:57:30.667Z] 08:57:30     INFO - GECKO(8684) | #17: NS_ProcessNextEvent(nsIThread*, bool) [xpcom/threads/nsThreadUtils.cpp:467]
[task 2021-11-25T08:57:30.668Z] 08:57:30     INFO - GECKO(8684) | #18: mozilla::ipc::MessagePump::Run(base::MessagePump::Delegate*) [ipc/glue/MessagePump.cpp:85]
[task 2021-11-25T08:57:30.668Z] 08:57:30     INFO - GECKO(8684) | #19: MessageLoop::RunHandler() [ipc/chromium/src/base/message_loop.cc:325]
[task 2021-11-25T08:57:30.669Z] 08:57:30     INFO - GECKO(8684) | #20: MessageLoop::Run() [ipc/chromium/src/base/message_loop.cc:307]
[task 2021-11-25T08:57:30.669Z] 08:57:30     INFO - GECKO(8684) | #21: nsBaseAppShell::Run() [widget/nsBaseAppShell.cpp:139]
[task 2021-11-25T08:57:30.670Z] 08:57:30     INFO - GECKO(8684) | #22: nsAppShell::Run() [widget/windows/nsAppShell.cpp:603]
[task 2021-11-25T08:57:30.670Z] 08:57:30     INFO - GECKO(8684) | #23: nsAppStartup::Run() [toolkit/components/startup/nsAppStartup.cpp:296]
[task 2021-11-25T08:57:30.670Z] 08:57:30     INFO - GECKO(8684) | #24: XREMain::XRE_mainRun() [toolkit/xre/nsAppRunner.cpp:5310]
[task 2021-11-25T08:57:30.671Z] 08:57:30     INFO - GECKO(8684) | #25: XREMain::XRE_main(int, char**, mozilla::BootstrapConfig const&) [toolkit/xre/nsAppRunner.cpp:5495]
[task 2021-11-25T08:57:30.671Z] 08:57:30     INFO - GECKO(8684) | #26: XRE_main(int, char**, mozilla::BootstrapConfig const&) [toolkit/xre/nsAppRunner.cpp:5554]
[task 2021-11-25T08:57:30.716Z] 08:57:30     INFO - GECKO(8684) | #27: NS_internal_main(int, char**, char**) [browser/app/nsBrowserApp.cpp:395]
[task 2021-11-25T08:57:30.729Z] 08:57:30     INFO - GECKO(8684) | #28: wmain(int, wchar_t**) [toolkit/xre/nsWindowsWMain.cpp:147]
[task 2021-11-25T08:57:30.730Z] 08:57:30     INFO - GECKO(8684) | #29: __scrt_common_main_seh() [/builds/worker/workspace/obj-build/browser/app/d:/agent/_work/1/s/src/vctools/crt/vcstartup/src/startup/exe_common.inl:288]
[task 2021-11-25T08:57:30.733Z] 08:57:30     INFO -  fix-stacks: error: failed to read debug info file `wkernel32.pdb` for `C:\Windows\System32\KERNEL32.DLL`
[task 2021-11-25T08:57:30.733Z] 08:57:30     INFO -  fix-stacks: note: this is expected and harmless for all PDB files on opt automation runs
[task 2021-11-25T08:57:30.734Z] 08:57:30     INFO -  fix-stacks: The system cannot find the file specified. (os error 2)
[task 2021-11-25T08:57:30.734Z] 08:57:30     INFO - GECKO(8684) | #30: BaseThreadInitThunk [C:\Windows\System32\KERNEL32.DLL + 0x17034]
[task 2021-11-25T08:57:30.746Z] 08:57:30     INFO -  fix-stacks: error: failed to read debug info file `wntdll.pdb` for `C:\Windows\SYSTEM32\ntdll.dll`
[task 2021-11-25T08:57:30.746Z] 08:57:30     INFO -  fix-stacks: note: this is expected and harmless for all PDB files on opt automation runs
[task 2021-11-25T08:57:30.747Z] 08:57:30     INFO -  fix-stacks: The system cannot find the file specified. (os error 2)
[task 2021-11-25T08:57:30.747Z] 08:57:30     INFO - GECKO(8684) | #31: RtlUserThreadStart [C:\Windows\SYSTEM32\ntdll.dll + 0x52651]
[task 2021-11-25T08:57:30.748Z] 08:57:30     INFO - GECKO(8684) | MEMORY STAT | vsize 2112852MB | vsizeMaxContiguous 65250467MB | residentFast 469MB | heapAllocated 166MB
[task 2021-11-25T08:57:30.748Z] 08:57:30     INFO - TEST-OK | dom/base/test/test_blockParsing.html | took 3093ms

https://hg.mozilla.org/mozilla-central/rev/dbb8dad0f657