As of yesterday, Firefox v38 became the lowest version (known as the Extended Support Release) supported by Mozilla.

Not only does this mean that it becomes the lowest version officially supported by Adapt - it also means you shouldn't need to include .ogv video files in your Adapt courses any more.

The main reason these were required was for Firefox on OS X which, until v35, didn't support MP4 video.

You can see the current state of MP4 support in the various web browsers over at caniuse.com