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.
On a device that supports PM, it will without a doubt have better software support. Current UbPorts runs on Ubuntu 16.04 base, so it basically can't run anything new until they fully migrate to at least 20.04