Example Problem: layout.css.devPixelsPerPx I somehow had the idea that things in about:config were also configurable via the userChrome.css. Is this true? Is it true, for example, with layout.css.devPixelsPerPx? If so, what is the equivalent CSS selector? Also, will changes to the css file over-rule changes in about:config, or vice versa? Answer: not much overlap From It_Was_The_Other_Guy1, it appears that there is rare overlay between the userChrome.css and the settings in about:config.

My userChrome.css doesn’t seem to be doing what it did previously, and the text in my URL-bar is far too small. Here’s what fixed it in my userChrome.css previously: #urlbar {-moz-appearance: none !important; font-family: Tahoma Bold !important; color: Black !important; font-size: 16pt !important; } but it doesn’t seem to be doing anything now; change the font-size and restarting Firefox doesn’t seem to make any difference. Why is it behaving differently now?

Version at time of writing: Firefox 79.0 First, locate your profile by going to the firefox menu bar: Help -> “Troubleshooting Information” and find on the page “Profile Directory”. Navigate there, where you’ll be making/adding two files that allow you to customize behavior and appearance of Firefox. For reference, mine was here: ~/.mozilla/firefox/aabkj82t.default/ . Yours will have some other blob of random characters before “.default”. userChrome.css This file should definitely exist already.