Font corruption inside Firefox (Search and Address bar) REVISITED
Going back to a previous question that never got answered, I also am seeing corruption in whatever font Firefox and Thunderbird are using for their UI font. I have searched for various fixes, but none of them do anything to change the font used for the Firefox address bar, or the emails listing in Thunderbird. At most all you find is how to change the font size or scaling, which is going to be useless if the font is corrupted (or the applications are not handling them correctly).
I'm figuring the way to verify whether it's a font defect, as opposed to a problem with the underlying code from FF & TB, is to change what font the applications are using, and/or to reinstall the particular font in question. So what is it using, and how do you edit that?
Firefox 90.0, Thunderbird 78.12 Fedora 34, Cinnamon Desktop