It works here with 128/W11. Does the same thing happen in safe/troubleshoot mode (hold Shift when launching TB)?

If you're doing this for all or most messages, it's possible to set display fonts permanently.

It didn't work in troubleshooting mode. I didn't know about that mode before, thanks. It's only emails from a couple of sources, but I get many emails from one of them. I tried increasing the font, but not sure I was in the correct settings as it didn't appear to do anything, even after reopening the program

Font in general ui:

• Menu app icon > Font size
• Use the + to increase to suitable size.

Font size in reading and writing messages - useful if you want them a bit larger than general ui

• Settings > General - images below as guide
• Scroll down to 'Languages & Appearance'
• click on 'Advanced'

• Fonts for 'Latin' to set up western encoding
• Set Proportional Size, Monospace Size and then Minimium font size (which must not be larger than the other sizes.)

whatever you set up for Proportional will be what Thunderbird uses as 'Medium'.

then select :

• Fonts for: 'Other Writing Systems' to set up unicode encoding
• Set all the same identical sizes as you did for the 'Latin'

then reset fonts for back to 'Latin' if that was your initial setting.

Repeat the above for any other options you use such as Cyrillic

• Click on Ok

In Settings > Composition

• Size: choose 'Medium'

Then when you compose emails if you set up Proportional as 14, then 14px will be Medium - the default size. If you wish to increase or decrease text then use the Formatting bar options.

The huge benefit of using the above means whatever you like to be as medium will suit you, but if your recipient has medium set up to be much larger because they might not have as good eyesight, then whatever they use as Mediun over rides it. This basically means you are sending emails which are user friendly.

When using zoom on messages, you need to select an email so it opens in eg: Message Pane then click in the opened email to ensure it has focus then use the Ctrl + + keys. It will not zoom on message if you have got focus elsewhere.

I did get the text in those messages to show up larger on opening. I reset the font sizes as you instructed. Had to go a size larger than I would have thought, but it worked. No more struggles to read what appeared to me to be 9 point font size! I did click in the opened email and tried the shortcut. That part still doesn't work. Must be some glitch between my machine and TB, though all else seems to work fine. Thank you so much!