This is actually pretty great. Youtube has some issue with Firefox 43 and serves it lower quality video to deal with it (probably as a hack to enable video for some users for whom it didn&#x27;t work at all under 43, but there&#x27;s no explanation from Youtube engineers in the thread). The Firefox team complains to Youtube, but Youtube responds with that they won&#x27;t budge until January at least.<p>Firefox sees it as a threat to their reputation (obviously for them having a few users for whom it doesn&#x27;t work is better than having loads of users with a degraded experience) and they start spoofing their UA to another version. The Youtube engineer is indifferent (or can&#x27;t really do anything about it).<p>Then when it&#x27;s done a Google employee from a different team comes in the thread to complain about the situation because the fact that the UA is spoofed for <i>only</i> youtube.com and not other (Google) domains breaks his product.