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

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.

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

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