Having the tab hiding API enabled by default means that Tab Group can finally come back and that we don't need to have a custom userChrome.css to hide the tab bar for Tree Style Tabs.

Tab hiding [0] is separate from tab strip hiding [1] unfortunately.

[0] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/AP...

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1332447

Aw snap, I though there were the same.