Hi paul381, is this problem on a Mac? If so, here's a very recent change: Firefox 91 now automatically enables High Contrast Mode when "Increase Contrast" is checked on MacOS. ([https://www.mozilla.org/firefox/91.0/releasenotes/ release notes]). '''Is it possible you have that setting?''' ''If so, please try one or both of these two options:'' (1) Turn off the system-level setting. This appears to be the most effective workaround. (2) Disable High Contrast mode in Firefox. See: [[Disable high contrast mode in Firefox]]. For both changes, you might need to Quit Firefox and start it up again to see the normal display. Any difference?