This bug is for crash report bp-b4a9e461-4bdf-4958-bade-2ebbb0200504.

Top 10 frames of crashing thread:

0 ntdll.dll NtWaitForKeyedEvent 
1 ntdll.dll RtlSleepConditionVariableSRW 
2 kernel32.dll SleepConditionVariableSRW 
3 mozglue.dll mozilla::detail::ConditionVariableImpl::wait mozglue/misc/ConditionVariable_windows.cpp:50
4 xul.dll nsThread::ProcessNextEvent xpcom/threads/nsThread.cpp:1140
5 xul.dll NS_ProcessNextEvent xpcom/threads/nsThreadUtils.cpp:481
6 xul.dll nsThread::Shutdown xpcom/threads/nsThread.cpp:909
7 xul.dll mozilla::net::TRRService::Observe netwerk/dns/TRRService.cpp:527
8 xul.dll nsObserverList::NotifyObservers xpcom/ds/nsObserverList.cpp:65
9 xul.dll nsObserverService::NotifyObservers xpcom/ds/nsObserverService.cpp:292

This is a shutdown hang waiting for sTRRBackgroundThread->Shutdown()
There are only a few reports, so it's likely not a big issue.
It's unclear if this is just a fluke, or there is something that's actually blocking shutdown.
In that case we should either fix the blocker, or if it's something that is hard/impossible to fix, we could consider leaking the thread (as we do for the DNS thread pool).