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It practically has, although they're still working on an API to hide the tab bar - until then, you'll have to hide it by editing a local CSS file.

There's also this annoying and useless header bar that's added to the top of the tab tree as well.

...which you can also remove with userContent.css file.

A port is available, it's a regression though. For example no native context menus.

I'm using Firefox Nightly and it let's me install it.

Tree style tab has been ported, it's a version that's a bit rushed but it does the job.