That would be this bug.

@Ed there is no fix within that link you provided. Subsequent to your reply I updated Thunderbird to 140.1.1esr (64-bit). after-which the zoom function and the background color began to work. Once I closed, then reopened T-Bird, the 'zoom' function broke itself again, when using the the combination of the 'ctrl' and the '+' key's; i.e. until/unless the view menu is used first.

I'm not sure what-else doesn't work, I don't have time to play with this.

Respectfully ...

The bug is fixed in the release versions but not in the 115, 128, or 140 esr versions. A quikcker 'fix' is to press F8, then ctrl + or ctrl -, then press F8 again and open the message in a tab. If you are having to increase or decrease a lot, you might need to adjust your viewing/composing font sizes. Let me know, it's easy to do.

@Ed hi, maybe three or four previous version's in the past, I tried changing the font-size, things didn't go well, is why I started using zoom on an as needed basis; never went back to see if the font-size issue was resolved. As far as the fix for zoom is concerned. I never checked the meaning/diffference of the different branches, i.e. 'Release' vs esr; I'll get on that right away.

First, in this current version I'll check if changing the font-size plays nice, if not, I'll go for the Release branch\version that includes the fix for the zoom function. Thank you for the heads-up.

Respectfully

@Ed hi, maybe three or four previous version's in the past, I tried changing the font-size, things didn't go well, is why I started using zoom on an as needed basis; never went back to see if the font-size issue was resolved. As far as the fix for zoom is concerned. I never checked the meaning/diffference of the different branches, i.e. 'Release' vs esr; I'll get on that right away. First, in this current version I'll check if changing the font-size plays nice, if not, I'll go for the Release branch\version that includes the fix for the zoom function. Thank you for the heads-up. Respectfully

This is how to adjust fonts:

- go to TB menu > Settings > General > Language & Appearance > Fonts > click 'Advanced' button

- at the top, set 'Fonts for:' to Latin if it isn't already

- change Proportional and Monospace fonts/sizes to your liking

- set Minimum font size to 14

- at the top, change set 'Fonts for:' to Other Writing Systems

- repeat the process of changing fonts/sizes

- at the bottom, make sure 'Allow messages to use other fonts' is disabled if desired > OK > close the popup

- set TB menu > Settings > Composition > HTML Style to Variable Width and Medium font

@Ed -- to be clear, I view my incoming using tabs; ctrl+ '+' will not work by default. I just discovered ctrl + '+' will work when I open msg's in a separate window. As for your reply, none of the recommended item\setting(s) affect inbox msg's opened in a tab.

Currently, I've set TB to open msg's in a 'new window' in which ctrl + '+' does in-fact work by default; 140.1.1esr (64-bit). I'll use this setting for the time being. I shouldn't have to pull you, or anyone else down this rabbit-hole. I'll have to make time to checkout the Release version of TB.

I will continue to monitor this thread should you or anyone else have a quick workaround.

PS where is the quote button for messages in this forum? I'm using FireFox ver: 140.0.2 (64-bit), the only reply controls I can see are: B, I, link and "bullet list".

Continued Respect