Surprised at all the negative comments here. I'm on macOS, using vertical tabs with a default theme and the UI is clean and just gets out of my way. Been very happy with Firefox since I switched a few months ago.
But then ... WP is not tied to one hosting provider. There are no shortage of hosting companies out there to which you can deploy WP. In fact, many make it so easy it is ridonc.
The sandboxing requires CF workers though, as it depends on V8 isolates. Seems fair enough, but it'd be nice to see easily deployable cross-platform support someday for isolates or something similar, and not just for emdash.
I used to use it (better mouse) before BTT added Logitech support - but wasn't really happy with it. Every single update changed something, mostly my cursor speed in some small, but sufficiently noticeable way and I had to adjust it every time, which was super annoying.
At some point my settings kept getting lost every time my mac went to sleep, and I had to restart the app all the time. I messaged the developer, but never received any response or acknowledgement and I just dropped it. It's a pity, because I did like it for a period of time while I was initially using it.