Check this for detailed instructions, but in short: It can change the tab colors, but I didn't have to use it for this purpose: I have FF theme set to 'System' and the system theme I'm using paints the inactive tabs (and the rest of the top bar) black even after the update to FF 89.īoth can be fixed. A more long-term solution is to use userChrome.css. The option to disable the new UI will inevitably be removed from about:config.