When Mozilla was initially experimenting with a mobile browser called [http://www-archive.mozilla.org/projects/minimo/ Minimo] many years ago it was actually on the then mobile Windows options. Mozilla then switched to developing mobile Firefox for the Android OS. There has been no mobile browser development for any Windows Phone's since then and not likely ever due to the tiny market share that is getting smaller over time. If Mozilla was going to make a mobile Firefox for Windows phones they would have done so for years, though I would not have been surprised if they discontinued development in last while if they did.