I would love to use firefox and kill my relationship with google chrome but this is by far my biggest issue with firefox - legibility at a glance.
For whatever reason, in Firefox only the active tab is coloured/marked and the inactive tab are transparent on the top bar. That is extremely problematic for me when I'm doing research for a project or simply have a lot of tabs open - I cannot read them at a glance, I can't see how many tabs are open because its just a sea of text. And the fact that I like my top bar to have a little pattern on it to brighten up my day is not helping.
I've tried extensions that would allow me to colour the tabs/create custom themes but they always only colour the active tab and never the inactive ones. And the fact that google does this by default and I don't have to bend over backwards for it is pretty good, ngl.
For reference, chrome: clear, legible, I instantly know what's going on
Firefox: uhhhh. yeah.
Whatever theme I use there is no option to make the inactive tabs a separate colour, they always blend into the bar.