This add-on modifies pages that use the new html5 tags for displaying video, as well as a few special cases, to use the old style of video embedding using the tag. This allows the browser to pass the video along to your installed plugins instead of trying to do it's own video rendering.
![System Video :: Add-ons for Firefox](https://cdn-ak-scissors.b.st-hatena.com/image/square/d7f5b1bbcd952d8675a65196fa5d0ecd536c42b2/height=288;version=1;width=512/https%3A%2F%2Faddons.cdn.mozilla.net%2Fuser-media%2Fpreviews%2Ffull%2F42%2F42565.png%3Fmodified%3D1530208725)