Can't agree more, have been using sidebery for about a month now, and even completely dropped chromium which I ran beside firefox for the last years to only running firefox with sideberry and container-tabs now.
Chrome is faster, snappier and works better on more websites I commonly use, but the fact that I cannot have "vertical tabs as trees" ruins the entire browser experience for me, so it's basically the only reason I use Firefox for the last decade or something.
[1] https://github.com/gorhill/uBlock/wiki/Blocking-mode:-medium...