Comment 40 for bug 434476

More and more video playback is now HTML5-based, and with all the effort to get rid of 3rd party plugins (also Flash), this would be a serious UX improvement. I uninstalled Flash and the screensaver is sometimes driving me nuts on YouTube.

Dummy keystrokes every 55s (see comment #10) sounds like an elegant cross-platform solution, no?
As this is open since 2009... time to take action? :-) Could any1 take this up?