New Firefox forks are quite interesting. I've tried it, these are my impressions so far:
The UI looks a little bit too much like a generic electron app to me, there is no option for native GTK or QT theming.
It seems they ship version that use the newer CPU instructions to optimize the application, I'm not sure standard Firefox does. This is neat. It does feel a bit faster but I'm unsure whether this is because of optimizations or because I have 100x as many tabs open on vanilla Firefox right now.
The vertical tabs are very nice. I currently use the "Tree Style Tab" extension and some hacky CSS scripts for that, and this seems like it would work a lot better.
The shortcuts are off by default, which is nice, but still seem to be the same as Firefox.
It feels a bit buggy. I had to restart the application to be able to load a site.
They kept Firefox sync, which I like.
You can choose between dark and light mode on the first startup, but I haven't been able to find the setting again.
Conclusion
Overall, a decent Firefox rebrand. Better tab management, split windows, and workspaces seem quite nice. I would probably consider using it if it put the settings in 1 place and didn't have any bugs.
I will likely ditch Vivaldi for this one tab groups gets implemented. It has all the features I need and I've been looking for a non-chromium browser to switch to for a while. Floorp was close but missing critical features. Zen is very exciting for me.
I am currently trying to see if I can replace Firefox with Zen. Zen still has some Firefox telemetry but they are off by default, so I like it. I think difference under the hood is DRM. Maybe it is time to finally ditch Netflix.
MASSIVE UI, like what? Why does the UI take half the screen? I specifically left Firefox for Floorp because of the massive UI, and then left Floorp for Vivaldi once I got addicted to Workspaces and saw that Vivaldi just does them better as they are really well integrated. Zen doesn't provide me anything of value, and actually takes away some. So, no thanks.
So far I really like it, some minor gripes like the private browsing window being hard to distinguish and Pocket being missing (I'm one of the 5 persons that uses it), but for that first one there's already a GitHub issue opened.
I've been using floorp but the vertical tabs is still quite clunky and it uses a lot of ram on linux compared to windows. So I'll try this right away and update my comment with a review.
Edit 2: I updated my pc and now it's pretty smooth. Will change the update after giving it a bit more time.
Edit 1: I used it and it needs time. Vertical tab is similar to floorp but it's too sensitive on "hover to expand". Webpages seem very laggy and clunky, I have auto scroll on and yet it feels very jittery. Takes less ram compared to floorp(~1gb) with 1tab. Themestore looks good. Overall looks quite modern. Final tldr, needs optimization and not ready for daily drive.