Earlier this year, we were surprised as anyone to learn that Sony Mobile is planning to launch a Firefox OS device in 2014. To show its intent, the company released an experimental Firefox OS ROM at the end of February for the Sony Xperia E (C150X). At the time we saw a short video of Firefox OS on the handset, but we’ve now come across a more detailed video (in Czech) giving a tour of the UI and features. To our eyes, the OS looks quite sluggish, perhaps not surprising given it is not expected to go live until next year. Check it out below.