Firefox on Windows is by far my favorite browser right now, as Edge had no noticeable features, Vivaldi is still in "beta", Chrome is overall slow and buggy, and Opera is just a clone of Chrome. However, I can't say the same for Firefox for Android. My phone is a Nexus 6 with Marshmallow 6.0, official stock ROM. If it helps, the Nexus 6 is the U.S. version, not the international. The issue is with playing any HTML5 video on the web with Firefox. When I first play the video, it plays correctly and looks good. However, if you give Firefox about 7-11 minutes while it is playing the video, the video itself just decides to glitch out, resulting in what appears to be a bunch of lines instead of the actual video. Audio still plays back fine. This is the result of letting a YouTube video play on for about 9 minutes. This happens with all HTML5 videos, not just the ones on YouTube. This glitch occurs on Firefox 42 for Android, Firefox Beta 43 for Android, and Nightly 45 for Android