In settings, I know it's possible to change the e-mails font size, however the UI font size doesn't change. This add-on increases the UI font size a little bit, but I don't think we should rely on add-ons to change something so basic.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.
I am about to stop using Thunderbird V102.3.3 due the inability to change the UI font size. Why am I squinting to read my folder names? Maybe because I'm getting older, but still, did you have to make the font so tiny with no way to change it Mozilla? Please fix this!!
No add-on needed
View > Font > ....
View > Zoom ... for just message reading
View > Density > ... to suit your taste
Font in folder tree and message list is really very small in daily builds (today 114.0a1 (2023-04-12) (64-bit), resolution 1920 × 1080.
This location, Connect > Ideas, is really about improvements. Breakage with Daily builds is better posted to https://thunderbird.topicbox.com/groups/daily/ or reported in bugzilla - both links are provided in the start page in Daily, Go > Mail Start Page. That said, you should expect transitory issues in an active development environment like Daily