TB very slow after reinstalling old version

[kleid]

I installed 78.something a few weeks ago, and did not like the way it looked or the fact that so many addons that I use are incompatible, so I rolled back to 68.12.1 (64-bit). This was quite difficult -- I can't remember the details but somehow I could not install 68 over the top of 78 because it created a brand new profile every time. Eventually I found a solution and I believe that I now have an intact version of 68.12.1 with my old accounts, emails, contacts, calendar events, etc. I'm not certain which files in my profile folder are restored from my backup and which were newly created by this installation -- I seem to remember that the new installation prevented me from just restoring the old profile folder in its entirety.

Ever since then, TB sometimes runs extremely slowly. For example if I click on a message header in a mailbox, the message takes ages to appear in the preview pane, as if TB is having difficulty communicating with the server. Or if I try to compose a new message or reply to a message, the compose window takes ages to appear. Quite often the rudiments of the window appear but it takes a long time for the whole window to load, e.g. the header area is visible but the details such as the To and Subject fields and the thin lines take much longer to load.

I'm now very reluctant to do anything to my installation in case I inadvertently get 78.something or ruin my profile in some other way and then have trouble restoring it. Furthermore, I'm not 100% certain that this slowness is actually to do with rolling back the version -- maybe it's just a coincidence and I'm imagining that they happened at exactly the same time.

I realise that I'm being really vague and can't put my finger on a specific problem, but can anyone think of anything that might be causing this behaviour and is fixable?

Thank you!

[DanRaisch]

How is the account set up, as POP or IMAP? In Thunderbird the menu path is Tools->Account Settings->Server Settings->Server Type at the top right of the dialogue.
What security software are you running on that system?

[kleid]

Hi, many thanks for responding.

All my accounts are IMAP. I'm running Avast. This setup has been the same for many years.

Also, just to mention, I have TB set up to compact all folders if it will save 20 MB in total, and I also manually compacted in case that helped, and I have also repaired the larger folders. Interestingly, the manual compaction told me it had saved a huge amount of space (hundreds of MB, I think), so I'm not sure why automatic compaction hadn't happened. Nonetheless, it didn't help...

[DanRaisch]

It's possible that Avast has gotten confused with the back and forth of Thunderbird versions. Have you rebooted the system since reinstalling?

[kleid]

Yes, loads of times. This has been going on for some weeks and I shut down most nights.

Avast is set to scan incoming email. In principle I could try disabling it for a few minutes at a time and see if it makes a difference.

In terms of other security, I've allowed TB through Windows Defender firewall.

[kleid]

I've tried to notice in more detail what is happening, and I believe this problem happens only with gmail accounts. TB tends to get stuck with a message "Loading message..." in the bottom left of the status bar. At this point I typically see my message list, and the selected message is highlighted, but there is nothing in the preview pane. Once the message does load, if I try to reply, TB is still very slow at loading a compose window. But I don't think any of this happens on accounts on other domains.

[tanstaafl]

See if http://kb.mozillazine.org/Performance_-_Thunderbird gives you any ideas.

[kleid]

Great suggestions -- thanks. I'll work my way through them!