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.
Want to mention that on GNU/Linux we also have Waydroid that provides Android app support :)
I know about that, but from my experience nothing really compares to the ease of use of the SFOS AlienDalvik. Though something may have changed since I last checked (1.5 years ago).
I mostly wrote it for other readers.
Also used both, I would say they are similar. But Waydroid can't forward notifications to the main OS as in Sailfish. Sad that AlienDalvik is not FOSS :(