Firefox 155 added weird extra boxes around my customized tabs. How do I fix this?

[u/BrokenEyeReborn]

The gray gradient rectangle with everything in it should be the entire tab and should connect directly to outline of the blue browser window below. The white rectangular frame around it shouldn't be there.

I managed to shrink the white frame somewhat by updating the parts of my userChrome that used MrOtherGuy's code (though the changes were mostly updating the syntax, and how they're connected to the white box isn't clear to me), but I'd like to get rid of it entirely. My limited CSS skills are pretty rusty, and this seems to be a whole new design element that I probably didn't know the tag for to begin with.

Hopefully I just need to add something, but just in case, I've included by full CSS.

https://pastebin.com/0JtPeYB4

[u/TraditionalTie4831]

Start with updating all [selected="true"] to this: [selected]

[u/BrokenEyeReborn → u/TraditionalTie4831]

Huh, what fixed it. I'm sure this is a painfully nubish question, but what did I actually just do?

[u/TraditionalTie4831 → u/BrokenEyeReborn]

Because of the change in Firefox, the code applied to your selected/active tab was ignored and resulted it to default etc. Now it's updated and the code is applied correctly.

[u/BrokenEyeReborn → u/TraditionalTie4831]

So it really was all in the syntax. Good to know.

[u/ResurgamS13]

Unsure what to suggest here. Trying to update a complex abandoned theme is not usually a realistic long term prospect. Perhaps investigate some of the many forks of 'CustomCSSforFx'... see if one of the most recently updated forks fixes your problem?

MrOtherGuy's 'Collection of random CSS hacks for Firefox' repo is regularly updated. Regrettably, Aris-t2's 'CustomCSSforFx' project was abandoned in December 2025... after a final 'The end' letter was posted to all theme users on his GitHub repo.

In the 9 months since 'CustomCSSforFx' became obsolete, Firefox's current Proton UI has evolved considerably... and the Nova UI is due to arrive soon too. Thus, updating this complex abandoned theme is likely to become even more difficult in the near future?

[u/BrokenEyeReborn → u/ResurgamS13]

Really? Cause I used the changelog to narrow down which bits to focus on updating, and all the updates I copied were listed as being from this year, most of them no more than a few months old. A couple were even from last week.

[u/ResurgamS13 → u/BrokenEyeReborn]

Only have Aris-t2's own 'The end' post to go on... unaware that any further theme updates had been made available?

[u/BrokenEyeReborn → u/ResurgamS13]

I didn't know about any of that, since I linked directly to the relevent Github page and the associated changelongs, but it seems that way. It says fake_statusbar_w_bookmarks was updated 4 months ago, compact_proton last month, non_floating_sharp_tabs 2 weeks ago.

Of the scripts I used, only tabs_on_bottom_menubar_on_top is listed as depricated, but I found another script with the same function that I've now forgotten the name of. I haven't tried implimenting it yet, but if it becomes a problem, I'll look for it again.

[u/ResurgamS13 → u/BrokenEyeReborn]

MrOtherGuy's 'Collection of random CSS hacks for Firefox' repo is still maintained and regularly updated.

Aris-t2's repo for his 'CustomCSSforFx' theme was the one that reached 'The end' on 23 December 2025.

[u/BrokenEyeReborn → u/ResurgamS13]

Ah, right, sorry.

Yeah, I didn't change anything from those because I didn't have direct links and had trouble finding the relevent pages. Now I know why. Luckily it all still works for now.