For the gui, try the Theme Font & Size Changer add-on. For message text, there is a better solution than using the zoom control.

More here: http://xenos-email-notes.simplesite.com/417754775

It says that Theme Font & Size Changer Ad on doesn't work on my (High Sierra, 5k imac 27") system.

Theme Font and Size Changer no longer works on TBird! When are the Mozilla developers finally going to understand that the default and only font size is ridiculously small, and at LEAST give users an option to use larger fonts??

The add-on worked for another user.

https://support.mozilla.org/en-US/questions/1198055#answer-1059537

Is there some critical difference between your hardware and that user's?

Hi Zenos,

I did see that it apparently worked for that Mac desktop user, but I don't know what differences there may be between that person's setup and mine, except that they have a 27" and I have a 21.5"

Perhaps they don't have the latest version of the Mac OS or TBird that I do, High Sierra 10.13.2 and TBird 52.5.2 (64-bit). As I said originally, this problem appeared only this morning on startup—I have most everything set to update automatically, so I don't know for sure if TBird was updated yesterday or this morning, if at all.

I've also emailed the Theme Font developer about this issue; I hope he actually replies.

Zenos said

The add-on worked for another user. https://support.mozilla.org/en-US/questions/1198055#answer-1059537 Is there some critical difference between your hardware and that user's?

Hi: I have all the latest updates and a late 2015 27" imac with an i7 and a 5k. I have been gratefully using the Theme Font addon for at least a couple of years. Just yesterday it seemed to stop working. The addons manager said I should go to their webpage for a new version that would work in the new environment, but the page said it would not work with my setup. I tried it anyway and the newer version didn't work either, as they had said. They had a little survey asking what I thought, shich I filled out.

I agree that it is ridiculous that the main Thunderbird program doesn't have any adjustments of this sort. I have the no small text addon which works on an opened email, but has to be done individually. Silly.

I have been using Thunderbird for many years, but I may have to abandon it over this issue.

The userChrome.css and userContent.css solution posted in the other thread should work for you.

https://support.mozilla.org/en-US/questions/1198055#answer-1059537

The solution described here was described in terms of Firefox (because the add-on no longer works in Firefox Quantum) but the technique works (or has worked!) in Thunderbird too.

my Thunderbird inbox list font went very small on Friday, January 5th 2018. The data of Thunderbird was December 24, 2017 52.5.2. I went back in MacOS 10.10.5 Timemachine and reverted to a December 4th 2017 52.5.0 copy of Thunderbird app. I still got the small font. I do not see the tool > ... item for Theme font & size changer for Thunderbird in neither version of Thunderbird.

Something to changed on my machine in the last day to cause a change in Thunderbird. What could it have been?

R