Yes, thankfully there's a nightly build[1].

Until there's a stable/signed release you have to allow unsigned extensions; set `xpinstall.signatures.required` to false.

To hide the default tab bar I needed to put the following in ~/.mozilla/firefox/xyz123-profile-here/chrome/userChrome.css

    #TabsToolbar > * {
      visibility: collapse;
    }

Some features, like autohide, aren't available with the new web extensions model, but otherwise works the same as pre-57 versions of TST.

[1] http://piro.sakura.ne.jp/xul/xpi/nightly/