When you install TST, it shows a message explaining to you how to get rid of the tab bar. It's also in their documentation: https://github.com/piroor/treestyletab/wiki/Code-snippets-fo...
Since the doc is not super clear on this, the userChrome.css needs to go in ~/.mozilla/firefox/*.default/chrome/userChroms.css (you might have to create the "chrome" directory).
It's not a super-nice process, but as someone who occasionally does tech support, I understand why they don't offer an API anymore that misbehaving addons could use to utterly destroy the browser UI.
It is also clear that this is a hacky workaround that is not guaranteed to continue working.
Mozilla, I'm going to use very small words here so that you understand: users will want to change your UI. You can't fight that without fighting your own users. Then again, that doesn't seem to be stopping them.
You can't both say "well we let you do it, we're so customizable" and "but if you do and anything goes wrong, it's your fault."
I'd rather that userchrome get removed and Firefox own up to the fact that they're not gonna properly support what users want.
A company who puts users first should not be ashamed of supporting their users' desires. You either support your users or you fight your users. Mozilla have somehow decided to publicly fight their users and furtively and abortively support them in secret; I really don't get how they think that reflects well on them. It feels like Moz are more trying to appease their own UX designers than their userbase.
FWIW Mozilla even experimented with vertical tabs, only they made the tab column so high it interfered with the URL bar and also didn't support nesting.
They broke the plug-in API years ago and haven't bothered to fix the new one meaning I'm stuck with ugly tabs on the top even when I use Tree Style Tabs. Scrapbook extension hasn't worked for years etc.
Today, the main reason I use it isn't technical superiority but stubbornness, idealism and rhe fact that the alternatives are just as bad. I.e. despite all the progress on speed etc nothing makes up for breaking the single reason why they were the work horse of browsers: the extensions ecosystem combined with cross platform and good baseline performance.
FWIW: Mozilla can get money from me today - if they promise to use it to fix Firefox.
They wont. Quite on the contrary they are quite clear that donation money goes to other projects. I understand this has something to do with Mozilla being a non profit and browsers development not being a thing in their charter, but sooner rather than later I hope they'll realize that providing a good, free browser is maybe the biggest thing they can do to secure an open web ecosystem.
I already donate money directly to other projects, so I am not interested in that.
I will be signing up for the VPN thing however once it becomes available and if I know the profits goes to Firefox (irony over irony is if I'll need to use a VPN to sign up for the VPN I want :-P)