I think it happened when I unchecked "Download remote fonts" in Firefox settings, but it refused to come back no matter what I tried, so... I guess a uninstall/reinstall is in order anyways!
In the end, the only reason I even bothered enough to reinstall was because I wanted to see Witches Town's upsidown purple stars for favouriting posts...!
Reinstalling fixed it, but. Y'know. I have no idea what the exact issue was. Fortunately there's not toooo much annoying with reinstalling