Mozilla never supported the mobile Windows Phones OS's with any version of Firefox and do not plan to in near future. The closest they did was with the Mnimo mobile browser experiment http://www-archive.mozilla.org/projects/minimo/ long ago before they then switched to Android. The mobile Windows market-share (reportedly went down to 1.7 percent market share in the third quarter of 2015) is not there enough for Mozilla to invest time and effort in it if they could even make it for mobile Windows OS. Mozilla is already making Firefox for desktop Windows, Mac OSX, Linux. Mobile Firefox for Android and recently the Firefox shell for iOS. They also have Firefox OS that can be used on some phones and is used by Panasonic on some of their Tv's.