How It Works
If your browser supports it, HTML5 video is used. No Flash—no crash.
HTML5 video in Firefox,Chrome
In other browsers that do not support
video, it falls back to Flash, or Window Web Media player.
If QuickTime is not installed, Adobe Flash is used. It’s important to note that the user is not prompted to install QuickTime if they don’t have it. Fallback is instant and automatic.
Flash fallback, (Flowplayer)
(which allows playback on the iPhone OS 2; OS 3 and above, Ipad use HTML5 video)
Firefox will only play OGG, and it will not degrade to Flash if you leave out the OGG video