I am using Firefox on Debian 10 (78.6.1esr) and my Japanese fonts got messed up after I installed a new font on the system. I installed the font into my Debian user folder, and it applied to everything as the default font. The fix was pretty easy, I simply removed it and everything want back to normal, except Firefox. Firefox for some reason is the only thing insistent on continuing to use the font, despite my font settings in Firefox set to use a more standard font. It wouldn't be so bad but the font in question doesn't have all the characters so the display is rather hideous in some cases. I tried to reset Firefox by renaming ~/.mozilla/firefox to ~/.mozilla/firefox.old, but the font remains. I've ran with it for about a month but I cannot take it anymore and have spent a days worth of hours trying to fix it. I've attached on image showing the display, and another showing my font settings. about:config does not show the offending font. Thanks!