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.