[Feature] Native vertical tabs

[reesericci]

Is your feature request related to a problem? Please describe.

Firefox has rolled out vertical tabs natively in nightly and I'd like it if this theme would support them. https://connect.mozilla.org/t5/discussions/firefox-sidebar-and-vertical-tabs-try-them-out-in-nightly/td-p/63231

Describe the solution you'd like

Styling similar to the tab center reborn integration

Describe alternatives you've considered

Additional context

[Tuxino88]

bad support

[rafaelmardojai]

bad support

There's an initial theming for the sidebar in the nightly branch, but vertical tabs are not supported yet.

[RushingAlien]

Hey 👋, as of firefox stable release 133, vertical tabs are now supported

[RushingAlien]

I think tabs close button should be disabled in vertical?

[rafaelmardojai]

@RushingAlien vertical tabs aren't still officially themed, since they still are behind the sidebar.revamp pref I'm not rushing.

They should look better now since I refactored the current code to only affect the horizontal tabs, but there's still plenty of work to do.

[malobre]

@rafaelmardojai FYI, sidebar.revamp was enabled for some users with the 133 update and it will be expanded to another "portion of users" in 134.

See this Mozilla Connect Discussion.

ps: love the theme ! Thank you for all your hard work.