I have a FF OS phone...
Alcatel one touch fire... for texts and phoning it is ok... but the apps suck balls, there are not enough of them. The other problem is that people write android and ios apps and let everyone else use a normal website. Which are FFOS apps... this sucks balls as most websites run badly on the phone. Mozilla's plan seemed to have hinged on everyone being willing to write a mobile version of their website... sadly that plan got ballsed up as no one seems to a have bothered. I use multicity car sharing from Citroen.... hardly small fry but even they only have an android and ios app... I get stuck with their desktop website that is completely unzoomable on such a low spec machine and completely unsable.
The only two apps I ever use are bbc news and the guardian... but as this is just a mobile version of their website it gets so bogged down with scripts and ajax loads that they just crash or you get asked if the tab should reload or just close... no "ignore the delay" option like on desktop FF... so half the websites with mobile frontends can never actually load as the hardware can't handle it... I could cry.
I won't be getting another one... I feel like someone who is using an OSS alternative to skype looks nice but completely pointless for chatting as everyone else is using skype and has no reason to swap.
Now I have received, about 8 months ago, an update... it broke shit loads of things... the apps crash every few minutes, there are huge memory leaks which means I have to restart the phone again - often, I now can't uninstall apps, the list goes on... and now no more updates... who knows when I will get another.
I tried a few apps and basically they are just experiments by bored web devs to see if they should bother making a FFOS version of stuff... some even require features that the phones from Mozilla don't have as they are low spec... I guess the devs were using some kind of geeksphone which came with better hardware.