Review for Theme Font & Size Changer (fixed) by Jayking
Rated 4 out of 5 stars
I found that if I uninstalled the add-on then re-installed it worked, well, partly... :) I couldn't select the arrows to manipulate the font size. So, I entered the number manually then hit apply and it worked for me via Thunderbird version 60 32bit.
This review is for a previous version of the add-on (64.4).To create your own collections, you must have a Mozilla Add-ons account.