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.
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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