I think I'm liking #ZenBrowser.
It's basically #Firefox but with vertical tabs, workspaces, and splits (and tab groups on the roadmap). After using it for a couple of days, I do feel like it's a better approach if the screen allows it. Splits aren't as necessary with a tiling WM, but still nice to have.
All my Firefox extensions work except for Firefox Color, which I used to generate a Firefox theme from my Emacs theme. I'll look into the browser's own theming mechanism if I stick with it; for now, there's a colorscheme which is close enough to my preferred `ef-duo-light'.
The browser is squarely mouse-driven out-of-the-box, but all the added actions (splits, compact mode, etc.) can be bound to keys. Even #Tridactyl seems to work without an issue, although I won't go through the pain of configuring the native messenger in Flatpak. I'll probably try to configure #Vimium, which would interfere less with the rest of the browser.
My largest doubt is about the project itself, though. It is not a fork but a collection of patches against the Firefox repo; there are 102 .patch files as of now. This is similar to #Librewolf, which, IIRC, had trouble keeping up with the upstream even with two core devs (until Dec 2023). Zen has one core developer. So, time will tell how sustainable the approach is.
Also, the repository weighs ~0.5GB even when cloned with `--depth=1'. I gave up on the full clone after it downloaded 1.2GB while still being at 0%. Something isn't right there.
https://github.com/zen-browser/desktop/tree/main