Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
I daily drove the ZTE Open and then the ZTE Open C for over a year each. Still have them kicking around in a box somewhere. Returning to Android was weird, but unfortunately there just weren't good alternatives, since Ubuntu bailed on Ubuntu Touch about the same time Mozilla pivoted away from FirefoxOS.
I've considered going with a Pine Phone, but not sure I want to go back to not having 5G support at this point. Kinda hoping that eventually we might start seeing more open alternatives once RISC-V matures a bit, but that's probably still quite a few years away at this point.