How would you do that latter part? I currently have a userchrome.css for something similar but I wasn't aware that you could have conditionals in css.

Using a different size for elements matching a :hover selector is how a lot of CSS gets this done.

The first result on Google (https://gist.github.com/olmstadfm/d6b4d37219e957d9cdcdb3ec88...) also seems to employ the :hover selector to accomplish hiding the tabs. I don't know how effective this particular script is, but it makes sense to use such a system.

Haven't had a chance to implement it, but this sounds rad. I never thought to use hover in userchrome.css!

Brilliant! Thank you!

Sidebery's wiki describes[0] a method using a window "title preface" API, then using that preface in CSS selectors.

https://github.com/mbnuqw/sidebery/wiki/Firefox-Styles-Snipp...

Wow, I should have read their wiki. Goldmine!

See here:

https://github.com/piroor/treestyletab/wiki/Code-snippets-fo...

Tabs like History and Bookmarks won't hide but TST does.

I don't know about TST, but sidebery can alter your window title when it's active, so you can match css rules against it.

    #main-window[titlepreface*="Sidebery"] #TabsToolbar {
      visibility: collapse !important;
    }

Oh heck! That's rad. I'll have to play around with that. I use sidebery so this is aces. Thank you!