User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

Open Thunderbird.
Try to scroll the list of messages.
Try to scroll an email preview.
Try to type anywhere.

Actual results:

Thunderbird freezes while checking email (or ... doing something?).
Things do not draw correctly (seems to be related to the freezing).

Expected results:

Thunderbird should not freeze.
Thunderbird should draw correctly.

I only just got upgraded (automatically) from 68.12 to 78.5 some time in November.
I have a Gmail account attached (but without the 2 huge folders "Sent" or "All Mail" synced).
I have some IMAP accounts attached.
I have Lightning + Provider for Google Calendar.

Waiting for Thunderbird 78 to "finish" whatever it is doing will improve things (hence why I think the redraw issues are related to the freezing). I expect to open Thunderbird and use it, not wait several minutes for it to think about things before I can use it.

Removing a message seems to cause the issue too, so perhaps it's an issue with server sync or .mbox file updates?

possibly bug 1677380

Or, do you have a 4k monitor? bug 1661980

I have a MacBook Pro 13" Early 2011. Screen is 1280x800 so ... not 4k.
The CPU load is not high at all. I have MenuMeters running so I do notice when something eats the CPU.
It's not that scrolling is slow, it appears to remain fast, it's just that the scrollable areas do not redraw properly.
I don't know how multi-threaded TB is, but it's like one thread freezes, then when the drawing thread need data, it fails so the wrong thing is drawn, while the UI input thread just blocks.

If I knew what to collect, I could get logs or something. I could probably screencap the app too, if that would help?

In that case, we might suspect bug 1677272

Well that was a roller-coaster of a bug report. Some of it certainly sounds similar... I gave that daily build a go:
https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/cS4TP33hS7yHdUx2l1zlyQ/runs/0/artifacts/public/build/target.dmg

It made a new profile... I copied (rsync) the old profile over the top (at least got all the email accounts/messages). I did not notice any issues.
I re-installed 78.5 to compare and ... didn't notice any issues with that either (old or new profile).

Hmm...

One major difference is that I'm running 10.11 (El Capitan), which is 5 major versions behind Big Sur. My issues were definitely caused by the TB upgrade rather than an OS upgrade. That other bug report... it's not completely clear to me that it wasn't an OS upgrade that triggered the report (but then, I only just got offered the TB 78 upgrade so maybe those reporters did too).

I tried a bunch of actions and the only thing that got close to reproducing my original report was when I scrolled around in the calendar. I noticed a freeze changing months... but it was just one freeze.

Perhaps the calendar or Google Calendar integration plugin (Provider for Google Calendar) is causing a freeze and that's the root cause of my issues? It refreshes every time Thunderbird launches...

I will stay on 78.5 to see if I notice issues in the future. Possibly I need to have email/calendar changes to sync in order to trigger the issue?

Let me know if there's any useful logs I can capture.

(In reply to Wayne Mery (:wsmwk) from comment #3)

In that case, we might suspect bug 1677272

That would be incorrect - this bug is not Big Sur.

That said, current beta has several Mac fixes available at https://thunderbird.net/#channel

I upgraded again, (and then again to 78.6.0).

I have had trouble reproducing the issues that I noticed originally, but I have noticed one more specific problem several times now.

The issue is that TB does not redraw at all. It has happened a few times, without apparent cause. Waiting did not seem to help but cmd-tabbing to another app and back did cause TB to redraw. I have seen this on both the Compose window and the Calendar tab.

This may be the same issue I originally noted, though I have not seen it on the main mail view, after upgrading again. Also, it didn't seem to be tied to TB doing anything specific...

Ooh, I just saw it happen on the main list view. Apparently in response to deleting a message.

I have TB doing IMAP to gmail and deleting emails has always done this little dance where the message disappears, then comes back, then disappears again.

In this case, the email went away, came back but the go away again didn't redraw.

Interestingly... mousing over the list view updated most of the entries (they were all moving up by one due to the deleted one being near the top), but not the last entry (which should have disappeared). The last entry was redrawn when I cmd-tabbed away, I didn't have to tab back before I could see it disappear (helpfully, the app I switched to had no windows open to obscure TB).

Saw it twice on the list view today, in fairly rapid succession. I was attempting to scroll the message list view (more messages than could fit). The first time nothing happened (as if the app was frozen, but cmd-tabbing away fixed it). Then it was scrolling up one entry, down one entry (very rapidly) so it was actually drawing, but not changing where the scroll point was. Again, cmd-tab away fixed it.

This was shortly after opening TB so may have been hitting the network to sync folders/calendars/etc.

I upgraded to 10.13.6, which is as far as my hardware can go. TB is now 78.13.0. The issue persists, and has maybe gotten worse. I regularly have to cmd-tab away and back to actually get Thunderbird to redraw its UI when scrolling lists, or entering text into fields.

I'm downloading the source code in the hope that I can find something in there that explains what is going on.

Erm... The website is offering me TB 91 but TB wasn't updating itself?
The website says 10.12 is the minimum version... maybe because I was on 10.11, TB blocked an update and got stuck?
I installed TB 91 from the website and the problem seems to be gone. I only gave it a few seconds so far but... I'm hopeful.

Glad it's working for you.
Note, Version 91 strictly speaking doesn't support macOS 10.11.