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.
We have GNU/Linux on smartphones now. There is PinePhone and Librem 5. Some Android phones can run GNU/Linux too.