Firefox OS doesn't get all that much attention. We've seen the OS running on some official devices such as the ZTE Open C, as well as on some unofficial devices such as the HTC Explorer. But more recently is a Firefox OS port for the Nexus 5.
The Nexus 5 Firefox OS builds are nightlies, however they are being described as highly functional. In fact, it was said the build is "almost a daily driver." Details coming from XDA member abtekk touch on how the main issues deal with the camera and WPA2. Specifically, the camera preview is broken and the build lacks support for WPA2-Enterprise.
On the flip side, data is said to be fine and the UI is described as being "buttery smooth." Touching back on the camera -- the handset will take pictures, it is just the preview that is broken. Still, we suspect that could be an issue for some. Anyway, those looking to run Firefox OS on a Nexus 5 should begin by making sure all the data is backed up before any flashing.
The flashing will need to be done through fastboot, and the Firefox OS download (link) is available from the forum thread on xda-developers. You can find the thread, titled; Firefox OS - Nightlies, using this xda-developers link.
VIA: xda developers