Hello everyone, I apologise for the long post. Today my Firefox updated to version 40.0, which now comes with the compulsory use of HTML5 for video playback instead of Flash Player. BACKGROUND: Prior to this update, I always chose to use Flash Player over HTML5 out of personal preference (and have always been happy with this decision). However, after the recent security issues with Flash Player, I had started to accept the transition to HTML5. Yet, after trying some YouTube videos with my new Firefox 40.0, there is an issue with HTML5 playback which makes me unhappy. SIDE INFORMATION: Before explaining the problem, kindly note that I run a Screensaver timed to activate after 1 minute. I have been using this setting for over 10 years because I find it a convenient way to lock my computer when I am away. ISSUE: Whenever I am watching a YouTube video (be it in New Tab or on Full Screen) and leave my mouse/keyboard idle, my Screensaver pops up after 1 minute. I have to move my mouse or press a button to bring back Firefox into focus. What bothers me is that, Flash Player always 'took priority' over Screensaver, regardless of the video length. With HTML5 it seems as if Windows reads Firefox as being idle during playback, and the Screensaver countdown is started. ADDITIONAL INFORMATION: Please note that my Shockwave Flash plugin is set as 'Always Activate'; it DOES activate when I play Flash Games for example. What is happening is that, as quoted on YouTube's HTML5 page: "The HTML5 player is currently used when possible". I did some research and sadly found responses such as "Disable your screensaver, it is useless" or "Other browsers do not have this problem". I really love Firefox, and have no intention of migrating to a competitor's browser, which is why I hope a prompt solution shall be found. Thanking you for your time.