You can also try these related scripts:

• YouTube Me Again! - ytma! automatically converts YouTube(TM), Vimeo, Vine, Soundcloud, WebM, and MP4 links into real embedded videos.
• video-element-rate-controller - add keyboard shortcuts that will increase/decrease the playback rate for video elements.
• Gfycat-Redirect gif to HTML5 - Redirects giant or fat.gfycat.com hyperlinks to their HTML 5 video counterpart
• GfyCat Redirect to WebM Video File - Automatically promotes GfyCat gif pages to raw WebM video
• gfycat redirect to mp4 - takes you straight to the file