Originally, Firefox had a dropdown menu that allowed the user to choose whether tabs were on the top, bottom, left, or right.
This has been an annoying trend with Firefox for some time. They take the default, expected functionality, marginalize it while saying "Users who prefer the old way can enable it in a setting / extension" and then the setting gets deprecated or the extension stops working.
See also: "Classic Theme Restorer".
All the while software that might work better as an extension is bundled with Firefox and enabled by default. e.g. "Pocket", "Hello".
Sidebery without using trees because they waste valuable tab name space. Having more name space is a key advantage to vertical tabs. I use separate windows for high level categories and use the titler extension to name the windows. Sidebery doesn’t recognize the titles when you want to move a tab to a new window though. That’s one of a few pieces of kruft in my setup.
Mozilla sucks, but it is because all of this should be baked in, not because of pocket or whatever political thing that HN regularly brings up.
I have tried the vertical tab implementation in several other browsers and they are all inferior. Safari’s is hilariously bad.
Not OP, but personally I'm using Tab Center Reborn with a bit of custom browser CSS to make it slide out on hover (so there are only favicons visible until hovered). It's just a vertical UI for tabs with handy filtering entry box, rather than a complex tab management thing like TST. The only thing I'm missing is filtering/jumping to the tabs that play sounds - it's easy to miss a tiny icon when you have thousands of tabs open :P
I use “tree tabs” and like it best due to its features like folders and unload-tab. However it is a pain in the ass to configure the theme to look right in dark mode. Plan on investing an hour. But once done is done.
Tree Style Tabs would be so great if it had folders/nodes for categories of tabs. My workaround are tabs with fittingly named Wikipedia articles, but a builtin feature would be more pleasant to use.
That I need to install additional extensions for features I wanted and also relying on those extensions to stay maintained. Also I don't like tree structuring generally, because I noticed that that just enables my tab hoarding habit. Configuration was also a bit annoying (in my memory) due to the drop down menus