So I applied an updated version of Firefox-UI-fix for Firefox 120, and now my accent on selected tabs is gone.
For context, this is what it looks like now -
The image below is in private window mode, because for some reason it works over there. Focus on the line above the selected tab, with a blue accent line. This is how I want it to be -
Here are my chrome and user.js folders.
try using Browser Toolbox to find the tab element, and then adding something like:
border-top: 4px solid blue
to that element in the userchrome css.
btw, enabling browser toolbox is a bit tricky, you have to enable “remote debugging” in the ctrl shift i settings, and then ctrl alt shift i to open it