After startup of latest debug build (after the account wizard has been filled out), I get an assertion failure and a crash (seen on windows and linux):

Assertion failure: mOwningThread == PR_GetCurrentThread(), at /builds/worker/checkouts/gecko/security/manager/ssl/CommonSocketControl.cpp:455

https://phabricator.services.mozilla.com/D167661 does not seem to be the cause and https://phabricator.services.mozilla.com/D168329 does not seem to help.

I do not yet know when this started.

 0:01.01 F:/mozilla/mozilla-central/obj-x86_64-pc-mingw32-debug\dist\bin\thunderbird.exe -no-remote -wait-for-browser -profile F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\tmp\profile-default -attach-console
DLL blocklist was unable to intercept AppInit DLLs.
[5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, NS_OK) failed with result 0x8000FFFF (NS_ERROR_UNEXPECTED): file /builds/worker/checkouts/gecko/toolkit/components/startup/nsAppStartup.cpp:911
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[ImapModuleLoader] Using nsImapService.cpp
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
Warning: unrecognized command line flag -wait-for-browser
[Parent 5456, Main Thread] WARNING: Failed to retarget HTML data delivery to the parser thread.: file /builds/worker/checkouts/gecko/parser/html/nsHtml5StreamParser.cpp:1234
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[WARN  rkv::backend::impl_safe::environment] `load_ratio()` is irrelevant for this storage backend.
[Parent 5456, Socket Thread] WARNING: NS_ENSURE_TRUE(inst) failed: file StaticComponents.cpcponsol:e1.5e5r7r6o
: (new UnknownCollectionError("Unknown Collection \"thunderbird/anti-tracking-url-decoration\"", "resource://services-settings/RemoteSettingsClient.jsm", 197))
[Parent 5456, Main Thread] WARNING: 'NS_FAILED(rv)', file /builds/worker/checkouts/gecko/netwerk/base/nsSimpleURI.cpp:618
JavaScript error: resource:///modules/DevToolsStartup.sys.mjs, line 696: TypeError: can't access property "parentNode", mainKeyset is null
console.debug: "Found 0 public keys and 0 secret keys (0 protected, 0 unprotected)"
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/toolkit/xre/nsXREDirProvider.cpp:478
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: (debug) mSafeStream->Finish() failed within nsBufferedOutputStream::Flush()! Possible dataloss.: file /builds/worker/checkouts/gecko/netwerk/base/nsBufferedStreams.cpp:988
[Parent 5456, Main Thread] WARNING: failed to save filter file! possible data loss: file /builds/worker/checkouts/gecko/comm/mailnews/search/src/nsMsgFilterService.cpp:230
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(uri) failed: file /builds/worker/checkouts/gecko/caps/BasePrincipal.cpp:1429
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: [l10n][mutations] Failed to start a refresh observer.: file /builds/worker/checkouts/gecko/dom/l10n/L10nMutations.cpp:249
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/chrome/nsChromeRegistry.cpp:180
[Parent 5456, Main Thread] WARNING: 'NS_FAILED(rv)', file /builds/worker/checkouts/gecko/chrome/nsChromeProtocolHandler.cpp:73
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(root) failed: file /builds/worker/checkouts/gecko/layout/base/nsDocumentViewer.cpp:2638
[Parent 5456, Main Thread] WARNING: 'aOwner->IsDiscarded()', file /builds/worker/workspace/obj-build/dist/include/mozilla/dom/SyncedContextInlines.h:95
console.debug: "Trying to load F:\\mozilla\\mozilla-central\\obj-x86_64-pc-mingw32-debug\\dist\\bin\\libotr.dll"
console.debug: "Successfully loaded OTR library F:\\mozilla\\mozilla-central\\obj-x86_64-pc-mingw32-debug\\dist\\bin\\libotr.dll"
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005 (NS_ERROR_FAILURE): file /builds/worker/checkouts/gecko/chrome/nsChromeRegistry.cpp:180
[Parent 5456, Main Thread] WARNING: 'NS_FAILED(rv)', file /builds/worker/checkouts/gecko/chrome/nsChromeProtocolHandler.cpp:73
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
[Parent 5456, Main Thread] WARNING: NS_ENSURE_TRUE(frame) failed: file /builds/worker/checkouts/gecko/comm/mailnews/base/src/nsMsgWindow.cpp:77
Assertion failure: mOwningThread == PR_GetCurrentThread(), at /builds/worker/checkouts/gecko/security/manager/ssl/CommonSocketControl.cpp:455
#01: uprofiler_simple_event_marker[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x6b30e86]
#02: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x72f0d55]
#03: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x72ef762]
#04: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x72fd773]
#05: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x72811e1]
#06: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x7324f6c]
#07: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x7323b40]
#08: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x729ada2]
#09: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x9d27662]
#10: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x1056f70]
#11: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x1056be7]
#12: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x1058839]
#13: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8915540]
#14: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8914d7b]
#15: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x890b2f9]
#16: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8902cdb]
#17: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8914e6c]
#18: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x89161d3]
#19: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x7706645]
#20: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x2daa45b]
#21: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362b7a7]
#22: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362b4b2]
#23: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362c121]
#24: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x361fe5a]
#25: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x361f51d]
#26: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x3621d30]
#27: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x3624f2f]
#28: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x1c8defa]
#29: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x2e1c5f4]
#30: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x30df750]
#31: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8915540]
#32: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8914d7b]
#33: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x890b2f9]
#34: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8902cdb]
#35: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8914e6c]
#36: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x89161d3]
#37: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x89172a7]
#38: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x784a2e3]
#39: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x78488f4]
#40: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x7640a3a]
#41: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x89098c0]
#42: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8902cdb]
#43: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x8914e6c]
#44: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x89161d3]
#45: XRE_GetBootstrap[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x7706645]
#46: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x2daa45b]
#47: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362b7a7]
#48: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362b4b2]
#49: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x362c121]
#50: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x361fe5a]
#51: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x361f65e]
#52: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x3621d30]
#53: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515ffa1]
#54: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515e75d]
#55: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x5158eea]
#56: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515ca81]
#57: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x35d9f45]
#58: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x35da1cc]
#59: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x35d6b47]
#60: VR_RuntimePath[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x35d50ad]
#61: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515e7e7]
#62: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x5158eea]
#63: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515877b]
#64: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515733a]
#65: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x515689c]
#66: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4cc7013]
#67: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4cc6d3b]
#68: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e4478d]
#69: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4cd5844]
#70: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4cd686b]
#71: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e458b3]
#72: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e487bd]
#73: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e46946]
#74: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e46504]
#75: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x296513]
#76: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e3c4c0]
#77: CallWindowProcW[C:\WINDOWS\System32\USER32.dll +0xe7e8]
#78: DispatchMessageW[C:\WINDOWS\System32\USER32.dll +0xe229]
#79: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e058a2]
#80: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4d32fa2]
#81: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x3fc156]
#82: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4032f5]
#83: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0xe8d911]
#84: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0xe12810]
#85: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0xe126cf]
#86: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4d32c78]
#87: soundtouch::SoundTouch::operator=[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x4e04e6c]
#88: workerlz4_maxCompressedSize[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x6e51128]
#89: workerlz4_maxCompressedSize[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x6fc334c]
#90: workerlz4_maxCompressedSize[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x6fc4b8f]
#91: workerlz4_maxCompressedSize[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\xul.dll +0x6fc53a8]
#92: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\thunderbird.exe +0x18f6]
#93: Ordinal0[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\thunderbird.exe +0x129d]
#94: TargetNtUnmapViewOfSection[F:\mozilla\mozilla-central\obj-x86_64-pc-mingw32-debug\dist\bin\thunderbird.exe +0x7e438]
#95: BaseThreadInitThunk[C:\WINDOWS\System32\KERNEL32.DLL +0x17614]
#96: RtlUserThreadStart[C:\WINDOWS\SYSTEM32\ntdll.dll +0x526a1]

Have not yet identified the offending commit, but somewhere in this window.

Bad 17.11:
mc: f85cd6ba1889c83b01c97d47a337caac6dcc1d8f
cc: 91e1e511f8e41b440be2db19167a49dc82eebf39

Good 16.11:
mc: efbd04cb07486419679cf588ba6095f7ef9edef6
cc: c1b5a7c88c0852e59815d98f54ab8d00c9b40a60

Setting up a POP account does not seem to fail, but setting up an IMAP account fails.

I think this is bug 1801067

It is.

Yes, M-C Bug 1791633 landed in that window and it very much looks like our port Bug 1801067 did not fully address the changes.