Native would be great, but for my use case the Tab Center Reborn extension for Firefox is the best implementation of vertical tabs I've used on any browser, native or otherwise. There's other extensions like Sidebery and Tree Style Tabs, but I haven't really tried them.

So you think TCR is the best one, but you haven't really tried the other ones? How can you know?

GP is clearly comparing their experience of FF+TCR with other browsers that implement vertical tabs (either natively or via extensions).

You're arguing against a strawman.

I’d settle for being able to turn off the unreasonably huge pane header that comes with extensions that implement vertical tabs via the sidebar.

Yes it can be hidden with userchrome mods, but it shouldn’t be necessary to resort to that, plus we don’t know how long userchrome mods will continue to work…

It took me a decent amount of work to finally get my sidebery visually config’d in a way that I found acceptable. I haven’t worked that hard on setting up an extension in a long time!

A little bit of userchrome.css magic fixes this. I use treestyle tabs and for mine I simply added:

#TabsToolbar {visibility: collapse;} #sidebar-header {visibility:collapse;}

Apparently Mozilla is working on that for over a year now (announced in Feb '22).