Further to the original question, the same issue applies to the main menu bar, and so it's quite a big deal.

I have no option to revert to the previous version as it was quite old, and I use the POP3 protocol.

I've never heard of this being a general problem, and I used that version long ago but I don't recall that ever happening to me. But it's such an old, version I doubt you'll find many people here who can check. Is there some reason you don't use the most recent version for your computer platform?

The first thing I'd try would be to turn of Hardware Acceleration, which can sometimes cause display anomalies and in my experience makes little performance different. In most versions that setting is found somewhere in Tools | Settings | General, but it may be different for your old version.

Did you see this symptom with the previous version? If you prefer to not upgrade, you could downgrade to the next lower MINOR revision (like, go from 102.15.1 to 102.15.0) to see if that helps. Old versions can be found here:

https://releases.mozilla.org/pub/thunderbird/releases/

Another thing to consider is to see if there are more recent or better display drivers for your computer.

Thanks a million Lin. That was the issue.

It's actually a new laptop, with Windows 7 pre-installed. I had to buy one because I spilled coffee all over my older one. I tend to be careful (or rather cautious) with upgrades because any little issue could halt my work progress. In this case, the upgrade happened automatically because I hadn't disabled it on the new machine.

The last version to support Windows 7 was 115.18.0 . Presumably it is the most "bug-resistant" of that series, so if you feel brave you could upgrade to that. I use it on my test Windows 7 computer and it works fine for me.

Of course, if you're happy with your current setup, there's no compelling need to change.

Also note the current version of Firefox to support the EOL Windows 7, 8, 8.1 is Fx 115.32.0esr and Fx 115.33.0esr out on Feb 24 will the last planned updated.