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.
I had a Windows Phone (NOT the older Windows Mobile) for a while back around 2011 thanks to my job as a multi-platform mobile developer. I loved that phone and the OS and developing apps for it was a lot easier and faster than for Android or iOS. I was surprised at how quickly Microsoft kicked the whole thing to the curb.
Nokia Lumia 700 in bright blue was stunning! I really liked it, the tiles were different and it felt funky. Pity they abandoned the project.