This is the relevant code to run video:
<video id="video" src="videos/clip.mp4" type='video/mp4' controls='controls'>
Your brwoser doesn't seems to support video tag
Video format or MIME type is not supported.
border:solid 1px #000000;
Firefox does not support the MPEG H.264 (mp4) format at this time, due to a philosophical disagreement with the closed-source nature of the format.
To play videos in all browsers without using plugins, you will need to host multiple copies of each video, in different formats. You will also need to use an alternate form of the
video tag, as seen in the JSFiddle from @TimHayes above, reproduced below. Mozilla claims that only mp4 and WebM are necessary to ensure complete coverage of all major browsers, but you may wish to consult the Video Formats and Browser Support heading on W3C's HTML5 Video page to see which browser supports what formats.
Additionally, it's worth checking out the HTML5 Video page on Wikipedia for a basic comparison of the major file formats.
<video id="video" controls='controls'> <source src="videos/clip.mp4" type="video/mp4"/> <source src="videos/clip.webm" type="video/webm"/> <source src="videos/clip.ogv" type="video/ogg"/> Your browser doesn't seem to support the video tag. </video>
Updated Nov. 8, 2013
Network infrastructure giant Cisco has announced plans to open-source an implementation of the H.264 codec, removing the licensing fees that have so far proved a barrier to use by Mozilla. Without getting too deep into the politics of it (see following link for that) this will allow Firefox to support H.264 starting in "early 2014". However, as noted in that link, this still comes with a caveat. The H.264 codec is merely for video, and in the MPEG-4 container it is most commonly paired with the closed-source AAC audio codec. Because of this, playback of H.264 video will work, but audio will depend on whether the end-user has the AAC codec already present on their machine.
The long and short of this is that progress is being made, but you still can't avoid using multiple encodings without using a plugin.