Well one thing you could probably do to speed things up is upgrade from the venerable Windows 7.

You could choose compact from the file menu to have Thunderbird remove all the old deleted mail that is probably clogging up your inbox and other folders. Folks do all sorts of silly thing with compacting like saying NO when the program tries to insist it is needed and then get upset when without basic housekeeping functions Thunderbird gets clogged drains. Compacting is not optional, even though the developers insist there has to be a user option to disable it. But then they do not have to field the user support requests that come from that decision either.

The next thing is disable any and all "mail scanning" in those ubiquitous anti virus things. They slow normal computer functions by about 30% with their actions and on email is can be significantly more than that. Especially if you get a lot of mail. I have seen individual emails scanned three or four times before anyone actually get to see them. If you just can not get by without it, disable it in the anti virus program and enable the allow anti virus to scan email in Thunderbird options. That way, each email is written into the temp folder of your computer and scanned by the anti virus before it is subsequently coped back into Thunderbird for storage in a mail folder.

You might consider preventing the anti virus from scanning the Thunderbird profile folders.. Nothing like having some other service trying to access the inbox file just when Thunderbird tries. "Not responding" is a frequent result of that kind of contention. This is significantly worsened if your storage files are large. 1 GB file takes about 10 minutes to scan, and if you get mail every 10 minutes, then the scanning and getting of mail fall over one another. Given the huge allocations of space Google, Yahoo and Hotmail offer folders of more than a 1 GB are becoming particularly comment as everyone becomes a pack rat and keeps everything for ever. I have even seen folk coming here with 6 or 120 GB inbox folders because they have no control over their own information and just expect software to manage it for them.

Then you can turn of windows indexing for the profile folders. That is in the windows file explorer window. Nothing like that brain dead windows indexing service to make my system slow.

Next disable the use of the option to allow windows to search your mail. That one is in Thunderbird options. That should make things faster and I never figured out what having windows search looking for mail was all about anyway. I did have to manually delete the 100,000 or so copies of email with the extension wdseml that were let behind when I turned it off.

Finally you can disable the Global search and indexer in Thunderbird options. This does disable the Ctrl+K search option, but it can make thing run faster.

Matt - thanks so much for the reply and suggestions...and comments. I do plan to update my 6 year old desktop soon and will say good bye to Windows 7 Pro. The culprit was definitely the anti-virus software as I was using Trend Micro. I ended up calling them and they immediately told me they had a newer version which was interesting as I had just downloaded a new version on 9/28...less than 3 weeks ago. But they re-assured me that there were "bugs" in that version and I needed to upgrade to their latest. After doing so, my email performance is back to "normal"...meaning it is working quickly~! I kick myself for not recognizing that this was an anto-virus SW issue all along. Thanks again for all your help.

I have the same problem.

I'm running Mozilla Thunderbird 78.3.2 (64-bit), on a 2015 MacBook Pro. Although not the fastest computer, it's certainly sufficient, especially after I upgraded it with a 2TB SSD drive.

There's definitely a regression. Nothing else on the computer is as slow as Thunderbird. It started with the most recent update. I didn't have this problem running the older version of Thunderbird that I had before (I think it was 75 or 76, I am not sure).

Has anyone else noticed this?

The spinning pinwheel is frequent. It almost feels like I'm using a remote web app, as all of the menu selections and scrolling up and down have about half a second of lag in them that wasn't there before.

It definitely is bothersome. It isn't related to compacting folders, or large attachments, or large mailbox folder sizes, because all of these things were true under the old Thunderbird version also. This problem surfaced when the new Thunderbird 78 version came out. I need to find a way to go back to the previous version.

I have the same problem.

Krellan, why are you spamming a topic where the author has already stated the problem was solved by updating Trend Micro?