I just tried it out and it's purely cosmetic - basically just puts your bookmarks bar to the left hand side, but it's not like rambox or opera or floorp. It just opens a new tab
i dislike horizontal tabs, so i go with sidebery / tree-style-tabs. also use a lot of pinned tabs and they sit on top of the list of tabs. this way i can have ~10 pinned tabs and still remember what all of these are.
the UI could be improved (I always end up hovering for tooltips on controls) but it works really well.
I also like that tabs will stay in the stash by default on close, so its great for opening a bunch of reference sites really quickly without worrying about losing them
Closest thing to the old firefox experiment from a few years back.
I use Tree Style Tab for the sidebar and Simple Tab Groups to get workspaces. They work quite well together. Customize userChrome.css to get rid of the sidebar header and other things and you get something like
I use the integrated sidebar, that comes with Firefox for viewing my pinned tabs. But it can only do that in this case and I'm assuming the sidebar on brave and Vivaldi can do more?