I got the following assertion from local xpcshell test run of TB.

Assertion failure: NS_IsMainThread() (nsXPCWrappedJS::AddRef called off main thread), at /NEW-SSD/NREF-COMM-CENTRAL/mozilla/js/xpconnect/src/XPCWrappedJS.cpp:241
Initializing stack-fixing for the first stack frame, this may take a while...
 0:47.90 pid:107167 #01: nsLDAPOperation::GetMessageListener(nsILDAPMessageListener**) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/comm/ldap/xpcom/src/nsLDAPOperation.cpp:189)
 0:47.90 pid:107167 #02: nsLDAPConnection::InvokeErrorCallback(int, nsresult, nsISupports*) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/comm/ldap/xpcom/src/nsLDAPConnection.cpp:0)
 0:47.90 pid:107167 #03: nsLDAPConnectionRunnable::Run() (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/comm/ldap/xpcom/src/nsLDAPConnection.cpp:688)
 0:47.90 pid:107167 #04: nsThread::ProcessNextEvent(bool, bool*) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/xpcom/threads/nsThread.cpp:1153)
 0:47.90 pid:107167 #05: NS_ProcessNextEvent(nsIThread*, bool) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/xpcom/threads/nsThreadUtils.cpp:548)
 0:47.90 pid:107167 #06: mozilla::net::nsSocketTransportService::Run() (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/netwerk/base/nsSocketTransportService2.cpp:0)
 0:47.90 pid:107167 #07: ??? (/NEW-SSD/ASAN-OBJ-DIR/objdir-tb3/dist/bin/libxul.so + 0xc17c36d)
 0:47.90 pid:107167 #08: nsThread::ProcessNextEvent(bool, bool*) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/xpcom/threads/nsThread.cpp:1153)
 0:47.90 pid:107167 #09: NS_ProcessNextEvent(nsIThread*, bool) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/xpcom/threads/nsThreadUtils.cpp:548)
 0:47.90 pid:107167 #10: mozilla::ipc::MessagePumpForNonMainThreads::Run(base::MessagePump::Delegate*) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/ipc/glue/MessagePump.cpp:302)
 0:47.90 pid:107167 #11: MessageLoop::RunInternal() (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/ipc/chromium/src/base/message_loop.cc:336)
 0:47.90 pid:107167 #12: MessageLoop::Run() (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/ipc/chromium/src/base/message_loop.cc:311)
 0:47.90 pid:107167 #13: nsThread::ThreadFunc(void*) (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/xpcom/threads/nsThread.cpp:393)
 0:47.93 pid:107167 #14: _pt_root (/NEW-SSD/NREF-COMM-CENTRAL/mozilla/nsprpub/pr/src/pthreads/ptthread.c:204)
 0:47.93 pid:107167 #15: ??? (/lib/x86_64-linux-gnu/libpthread.so.0 + 0x8ea7)
 0:47.93 pid:107167 #16: clone (/lib/x86_64-linux-gnu/libc.so.6 + 0xfdd8f)
 0:47.93 pid:107167 #17: ??? (???:???)

There are bugs related to AddRef called off main thread.
bug 1688838,
bug 1517400

I think this needs fixing a la bug 1688838 (?)

This is a thunderbird issue.
Objects implementing nsILDAPMessageListener are not threadsafe. So they either need to be made threadsafe, or this operation needs to be dispatched through the main thread.

(In reply to Valentin Gosu [:valentin] (he/him) from comment #1)

This is a thunderbird issue.
Objects implementing nsILDAPMessageListener are not threadsafe. So they either need to be made threadsafe, or this operation needs to be dispatched through the main thread.

Thank you for the explanation.
We will find out who can take this on. Hmm...