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.
It still exists but only officially supports google nexus and some niche phones. I don’t think it’s going anywhere but I do hope to be wrong someday. At the moment there are options like GrapheneOS to run Android without letting Google into all your shit by default.