Embedded vimeo videos can't be run in fullscreen mode in Firefox Once when I opened a Vimeo video in a fullscreen mode, I was prompted whether I want to allow Vimeo to use fullscreen mode. I checked "do not ask again" and clicked "No" by accident. It was embedded on a website and now I can't view embedded vimeo videos fullscreen in Firefox. However, when I go directly to a vimeo.com website, fullscreen works.

How do I remove Vimeo from the Firefox's blacklist?
In the menu : 

Tools > Page info > Permissions > Check Fullscreen mode.