Poor quality on h.264 file playback

Working with mediaelement 7.x-1.2, and the newest MEjs build as of today, I find that playback of H.264 files is poor. The image quality is blocky as if the pixels are really huge or it is highly compressed. I find this problem with Firefox, but on Safari on Mac OS X is perfect. Any ideas why this might be happening?

Here is the link to the page running MEjs playback, followed by a direct link to the file.

http://www.cctvcambridge.org/prompt

http://www.cctvcambridge.org/sites/default/files/video/Prompt%20Communic...

And here is a screenie of the bad playback on Firefox...

Would appreciate any help!