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 seems that the main complaint is calls and SMS. I use different distro (Arch, btw) with FOSS firmware for the modem and calls / SMS work fine for me.