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I'm running Ubuntu 14.04, Mozilla Firefox 29.0 for Ubuntu Canonical 1.0.

After installation I've watched some YouTube videos and clicked fullscreen, and the popup 'allow full screen?' appeared. By misclick I've clicked 'Don't allow' and 'never ask again'.

Where is this information stored? How can I reverse it? It's very annoying since I can't view embedded YouTube videos in fullscreen until I repair it.

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up vote 12 down vote accepted

If you were using YouTube's HTML 5 player (as the "never ask again" in the popup suggests), the fullscreen setting is managed by Firefox (and therefore has nothing to do with Ubuntu or Gnome).

Go to about:permissions (just copy it into your address bar), select from the list and change the setting in the Fullscreen box.

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Thanks, I'll try it as soon as I get home – fetta May 12 '14 at 8:25
still works, great, thx. – mondjunge Jun 25 '15 at 14:37
I just had this in Firefox 40. I had to restart firefox before youtube was listed in about:permissions. Also fullscreen was still listed as always ask. Selecting "block" and then "always ask" again fixed it. (Perhaps a new bug in 40, it was released this week) – Julian Stirling Aug 17 '15 at 3:36

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