I don't see anyplace to fix this, but for awhile now it seems whatever font Firefox uses for its own needs (Search and Address bar) is corrupted. I tried changing my settings but that doesn't seem to apply to this area so nothing changed. Basically I can't read the address bar text because there are missing letters, and I am seeing some corruption in the search bar as well. If I highlight the text, suddenly it's OK, but otherwise it's gibberish. It reminds me of LED signs where some of the bars might not be lit up so you get only a partial display.