firefox_49.0 is now available for download/upgrade from main. This is available for MX15/14 and M12.
Release notes: https://www.mozilla.org/en-US/firefox/49.0/releasenotes/
In this release MX15 user should be allowed to watch Netflix. In order to get this to work a user-agent switcher will still need to be used. I set it to Google Chrome and Linux and Netflix now plays. I used the following addonhttp://mybrowseraddon.com/useragent-switcher.html
Also when once you enter Netflix a small dialogue box will drop down underneath your address bar/bookmarks bar and will want confirmation that you do want to install the components needed to watch Netflix.
I was unable to get it to work on either M12/MX14. In M12 Netflix seemed to just load and load, but on MX14 the widevine plugin would crash. These tests were done in a VM so maybe you can get it to work on a real hardware install. If so please post how so that other users are able to benefit.