There are dozens of posts here talking about Theme and Font Changer add-on not working with the new Thunderbird version. Go ask the add-on author when they are going to do an update that their software.

Since you are obviously aware of "dozens of posts" regarding this same problem, and since I don't know how to contact the "add-on author", perhaps you could ask the author the same question....it would probably carry more weight.

Try this modified version of the add-on:

https://www.dropbox.com/s/e2sc3gr4mogsi0h/theme_font_size_changer_for_thunderbird-62.0-sm%2Btb.xpi?dl=0

Zenos said

Try this modified version of the add-on: https://www.dropbox.com/s/e2sc3gr4mogsi0h/theme_font_size_changer_for_thunderbird-62.0-sm%2Btb.xpi?dl=0

It's 404!

I think that was a temporary link for the months old post you are reading. Try this one. https://addons.mozilla.org/en-us/thunderbird/addon/theme-font-size-changer-fixed/

docmeyer3 said

Since you are obviously aware of "dozens of posts" regarding this same problem, and since I don't know how to contact the "add-on author", perhaps you could ask the author the same question....it would probably carry more weight.

To docmeyer3 I missed your reply so here is your answer.

All support is provided by Thunderbird users that volunteer their time to answer questions. I do not use Theme and Font changer. I really do not care if it works or not. I am aware of all the posts due to spending several hours a day trying to help on this forum.

Me asking the author means nothing more than someone like you who actually uses it. You chose to use a 3rd party add one and that software is supported by the software author. You seemed to be able to find the link to download the software you should be able to find the button with the simple word SUPPORT on the same site.

https://support.mozilla.org/en-US/questions/1213520#answer-1100279