How to block html5 videos system wide

Solution 1:

How to disable Video in FF

In the comments for this enhancement request there is a suggestion (comment 5 at 2012-03-13 15:57:41) to set media.webm.enabled, media.ogg.enabled and media.wave.enabled to false in order to
"render <video> and <audio> elements unable to play anything."

All these options are readily available if you enter about:config in the address box, and then enter media. in the filter box. In my testing (Firefox 10.0.1 on Gentoo) it was not necessary to restart Firefox, the elements were disabled when I reloaded the page.

This page was useful for my tests. The video there is disabled when both media.webm.enabled and media.ogg.enabled are set to false, as there is fallback from one to the other.

Source

How to disable HTML5 in IE

Adding a site to the compatabiltiy sites list disables HTML5 on that site.