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 remember using multiROM to install Lineage OS, Sailfish OS and Firefox OS all at the same time on my Nexus 4. I wished there was some kind of software today that you could dual boot an android phone.