Firefox OS was pitched as a direct competitor to iOS and Android, which itself was a death sentence when you saw the kind of hardware it was launched on. "Severely underpowered" would be generous. Plus they launched at a time when mobile web (that FF OS depended on for app delivery) features were awful compared to native apps.

Their timing was poor too. The market was saturated with alternative OSes back then and not enough PR oxygen to go around.

- Nokia Meego OS

- Windows Phone

- Blackberry Playbook OS/BB10 OS

- Sailfish OS (ex-Nokia people)

- Ubuntu Touch OS - WebOS