Just to clarify: the other menus (File, Edit, View, etc.) are all fine. It's only the main "Thunderbird" menu that doesn't seem to do anything. And "Command-Q" works, so I have an alternative to "Force quit...". However, "Command-H" doesn't hide it, it just makes the Thunderbird menu flash.

The same thing exactly is happening to mine following an upgrade I am on 10.15.2 OSX and 68.4.1 on Thunderbird.

I've reported this as a bug now: https://bugzilla.mozilla.org/show_bug.cgi?id=1608893

Great thank you

Has there been any progress on this? I have exactly the same problem. The worst of isn't being unable to quit. It is that I cannot access Preferences to change anything.

It appears to have been fixed in the daily build, just not the released versions. See the discussion in the bugzilla link https://bugzilla.mozilla.org/show_bug.cgi?id=1608893

I think there was a release since Jan 14 and I think I installed it, but since I can't access "About Thunderbird", I'm not certain I'm using a newer version.

you know I think you guys may well be talking about two different things. Certainly the testing is was only done onV74, and the bug has not moved to new from the unconfirmed status that initial report receive.

Have you tried rebuilding the global database? It has worked for lots of non OSX folk that have had no mail appear in the user interface and malfunctions on the main menu bar, like troubleshooting information being inaccessible. https://support.mozilla.org/en-US/kb/rebuilding-global-database

The linked instructions to find the global database didn't work for me, so I haven't tried rebuilding it. As far as I can see, I have no files named "global-messages-db.sqlite" in ~. (In fact, none match "global-messages".)

Whoops, found it. Will let you know.

I'm currently rebuilding, and it hasn't made any difference to the menu. Rebuilding finished, but no difference.