If you have a higher-than-full-HD display, several affected users have reported that the controls of the Flash player do not scale up automatically. Users have reported two workarounds for this issue, at least on YouTube: (1) The YouTube Center extension: https://support.mozilla.org/questions/1005923#answer-590458 (2) Switch to HTML5 on YouTube (this will cover many videos, but some will still use Flash): https://support.mozilla.org/questions/982635#answer-520300 I don't recall seeing any workarounds posted for other sites (but it's impossible to read or remember everything posted here). Now... for the problem of the HTML5 player not offering 1080p streams, you could try the steps in this article: http://www.ghacks.net/2014/07/30/play-1080p-videos-youtube-firefox/ Does that work for you?