HAVE YOU TRIED ARC? CLOSED SOURCE BUT WOW VERY UNIQUE UX
Do you know Zen? https://github.com/zen-browser/desktop
It's a Firefox fork with some interesting UI/UX ideas. Currently test-driving it next Brave as my current default browser.
Discussion
Don’t think I used it, tbh. Wouldn’t touch it because of this:
> Users are only able to use the browser after signing up to an Arc account with an email address.
Uses Chromium so v2 extensions are probably dead, so no uBlock.
Also, Ark vs Zen 👀:
LibreWolf has the same vertical tabs option. but it doesn't handle containers as well as Zen. that's the big win with Zen