It may help to post screenshots of your font settings in Latin menu and in Other Writing Systems menu.

Two screenshots of the font settings in Latin and Other Writing Systems, plus one of a "Finder" window showing the strange fit of the three window-handling button-dots in the upper left, the tiny text of the message-body and Confirm window from within T'bird, and the other places (Window Menu, From) where the text is normal-sized (with Subject larger from within T'bird settings).

The tiny text in messages will zoom up just fine in T'bird, but that's a nuisance for every message (and a strangeness mystery and challenge).

This strangeness started upon migration of T'bird from my old 2013 iMac running MacOS 10.15.n to a 2019 Macbook Pro running MacOS 15.3.1, with the iMac using T'bird 123 or later and the MBP running T'bird 128 (but I am not sure because it is too small for me to read and I can't zoom it). I suspect some dissonance between T'bird and the OS, but all my poking around in MacOS System Settings and changing settings have not resolved this.

All messages, even from long before the migration, are displayed this way.

One clue might be the About Thunderbird window in "Finder," also with tiny text from T'bird in a normal-text window-frame.

I like to pretend that I know my way around Macs and apps, but this one has humbled me.

Please advise.

Thanks, Alexander

That is approx 12 point font. I suggest upping the number to 20 for latin and other writing systems and try that. Many assume the numbers are points, but they're actually pixels. Try and let us know.

I tried that; it makes no difference within message-text fields, but it does change text in the frames. Only the top SIze box will go above 16.

Also attached now is the hamburger-menu screenshot, just in case that tells us something.

And this might be another clue...

OK, I'm confused. You indicate (I think) that font size of messages is ok, and you also show that font size of non-message fields can be made quite large, so what is the exact problem??

Hello Alexander, all your screen shots are misleading since they are displayed much bigger in forums than the original. By default recent macOS versions use a 144 pixel per inch resolution in screen shots versus 72 pixel per inch in earlier versions. I have noticed that when I purchased my first iMac with a Retina 4k screen. All my screen shots were blown up when I sent them or used them in forums. Since several years I regularly edit my screens shots with Preview to resize the images to 50% of their original size. As an exemple I'll show two screen shots of the "About Thunderbird" window, one in the original size and the second resized to about 50% of its original width.

The 3rd image shows my font sizes for Latin, Other writing systems are the same. The 4th image corresponds to your screen shot of a received message displayed in a new window. Maybe you could emphasise with a new screen shot where exactly you need greater text.

To David: The "Tiny Text" screen shot of your message is typical: The text in the message-field is tiny and I don't know how to make it larger, while the framing window-texts are large (and I can make those larger and smaller). And the three window-handling button-dots in the upper left corner fit weirdly into the window-frame. the window.

Similarly, the four column-head icons on the far left of the inbox are tiny, while the text column-headers are large.

And Mapenzi, both those "About Thunderbird" images look identical on my screen. And the screen-shot of David's message shows where the anomalous tiny text is. And in the shot of the To: field pull-down, the To: field text is large while the pull-downs are tiny.

None of this was like this before the migration, which is why I intuit some OS/T'bird dissonance (but that's a guess).

In the Fonts setting, I have the top size set to 22 and the others to 16 (the highest those two go) for both Latin and Other. Still too tiny.

I am in "a little knowledge is a dangerous thing" mode, and it seems this situation is vexatious for you guys, too.

I admit, this is puzzling. Haven't seen this before. Below is a setting that applies globally, so use TINY increments in experimenting.

1. exit thunderbird
2. first make a copy of prefs.js, just in case you have problems.
3. click tools>settings>general and scroll down to config editor on right side.
4. enter layout.css.devPixelsPerPx the default is -1.0 try increasing slightly, as it can quickly get too big. try something such a 1.2 or so for starters.
5. If still too small, increase just a tiny amount, such as 1.8 or 2.0. If you increase to the point that thunderbird is impossible to read because font fills the screen. that is your clue to exit thunderbird, restore the backup of prefs.js and start over.

If you're not sure how to locate prefs.js, do this

1. - click help>moretroubleshootinginformation
2. - scroll down to 'Profile folder' and click 'open folder'
3. - exit thunderbird
4. - make copy of prefs.js
5. - restart thunderbird.

@ Alexander: I have tested your font sizes 16 / 16 /16 px for Latin and Other writings and made screen shots of the same message, first displayed in the "message pane" and then in a new window. Results in my images below. With "your" values I can't see any "tiny" text except for the message headers which I have customized with a userChrome.css file.

I propose to start TB in "Troubleshoot mode" https://mzl.la/3AbU5jz and verify if you have the same problem with tiny text and eventually test bigger sizes in your font settings.

David, I have juggled the parameters you suggest (and it's an elegant UI, with different parameter-lists in separate tabs, with adjustments appearing in real-time in the others).

A couple of details: the default I found for the "layout.css.devPixelsPerPx" parameter was 1.3 not -1 (which is the default for the parameter just below), and I changed it variously up to 2.5, settling in at 1.5 and changing all the General: font sizes/writing systems all back to 14. I also noticed that the 'User Agent" datum in Application Basics in Troubleshooting reads "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:136.0) Gecko/20100101 Thunderbird/136.0". MacOS 10.15 was the OS I was using on my older iMac that I migrated-from, while this less-old MBP is running MacOS 15.3. Is that perhaps a source of dissonance?

Just below is the OS datum, and I don't know what Darwin 24.3.0 etc means, but the date in tht field is right around when I installed the current OS on this machine.

This setup is now workable, with the actual text size in messages still proportionally tiny compared to the message-frame text (especially the enlarged text of the "Subject:" field, which I somewhere made larger but now can't find where I did that, so I have left it too big — please advise).

Here are two screen-shots, the first (AC T Inbox 14Mar.png) showing the framing text for the inbox and mailboxes, and in particular showing the anomalously tiny icons atop the Read, Thread, Star, and Attachments columns. How can those be made appropriately larger (and maybe more bold in the columns)?

The second (AC TB Messages Font Sizes.png) showing the relatively tiny (but a bit larger than before) actual-message-text size compared to the message-frame text. Also note that the three window-control buttons are still jammed into the corner of the window, but less chopped-off than before.

I am using the original prefs.js. Seems I don't need the copy.

I have not created a new profile, since this is now a bit better. Would it still make sense to do that? I would need detailed steps like you have provided for the other modifications.

The challenge now is to bring up the message-body text size while leaving everything else as it is now.

I have to wonder if some of this behavior is from bugs in the code (which I reckon has become very complicated), and not just from strange dissonances in my setup.

Thanks for your patience and support through all this. Maybe some of it turns into addressing some subtle and obscure bugs and simplifying the code.

A.

A couple of details: the default I found for the "layout.css.devPixelsPerPx" parameter was 1.3 not -1 (which is the default for the parameter just below),

In my Thunderbird installation on macOS the default value for "layout.css.devPixelsPerPx" is -1 (image). If I change the value to 1.3 I get the same problem with tiny text as yours ....

On your two questions: - no, you do not need another profile. all your changes are in this one - to adjust message font size, see my earlier response on latin and other writing systems, under settings>general. The numbers are pixels, not points.

Mapenzi, I have no idea how that proper default of -1 for the "layout.css.devPixelsPerPx" parameter became 1.3. I had never been into that layout until I followed your directions. Maybe something else I messed with triggered that change, or maybe some random dance of electrons did it, but we'll never know. So that is a mystery.

I changed it back to -1, and the whole mess cleared up, including the tiny icons and the buttons in the upper left corner. I am back to a usable UI for TB, and I am so very grateful to you and David for saving my ass on this one.

And David, yes, I went back and re-adjusted the settings for Latin and Other writing systems, and that finished the job.

We now get to click the "Solved the problem" box...

Great news! Free beer for everyone. Thanks for the feedback.