What is your anti-virus software?

McAfee, which I've been using for 8+ years. Since originally posting this problem, I've 'repaired' all my larger folders and doubled the size of my TB cache. I think the cache might have been the source of the problem, more than repair, but it will take me a few days to verify if the problem has been fixed.

thank you Christ1 for your quick reply.

It's unlikely the cache is the culprit. See https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#McAfee

Christ1, Thanks for the link. I don't have the McAfee add-in for TB, although I do for Mozilla. Do I need to check settings within McAfee? The problem is not in opening TB per se, but in moving about after it is open.

TB version 24.6.0. Compact Header 2.0.8 Addin Lightening 3.3.1 Add-in

I have a few others (about 8 total), e.g. Thunderbrowse, but don't think any of them could be part of the problem.

That's probably a good idea.

Correction, I do have two McAfee plug-ins; Security Center 12.8.957.0 Virtual Technician 7.1.0.2483

The plugins are not the issue. In most cases of simple slow response it is a need to set McAfee to scan programs and documents instead of everything.

For reasons best known to McAfee they scan ever file as it is opened and as it is written to. Thunderbird uses files in the gigabyle range in size. This takes anti virus programs (any of them) minutes to scan. So Thunderbird is left waiting while the scan occurs and at times a timeout message appears as the process is not set up to wait as long as the scan takes. scanning of all files is not necessary and when people go to McAfee complaining of slowness, the first thing their online support people do is change all files to programs and documents.

I think I was able to resolve this problem thanks to the help from Christ1 and a little bit of creativity on my part.

I don't think this solution addressed my unique circumstances, but may be applicable to other users. My McAfee scan setting was on a weekly basis, but the TB issue was a daily occurrence.

I did follow Christ1 and your suggestion to tweak the McAfee settings related to e-mail scanning, doubled the size of my cache from about 350 to 700, 'Repaired' any folders containing more than 50 e-mails and archived a number of older folders that are no longer in use.

One or some combination of these tweaks appears to have solved the problem. Since the original post yesterday, TB seems to be much faster to load and more responsive to opening, deleting and moving files, but I have not been active enough all day to see if any of the (Not Responding) errors return.

If the choking problem persists, I will re-update this posting chain, Otherwise, assume problem solved

Once Again, to both Christ1 and Matt, I really truly appreciate your prompt & helpful responses to my many queries: I'm not worthy ! I promise to make a donation to the Mozilla Foundation in your honor to keep such quality support alive. Best