As mentioned in my previous answer, you might also want to consider including a webm version and/or an ogv version of your file, depending on which browsers you want to support.
Currently you are only including your film in mp4 format and Firefox does not support this.
Here's a compatibility chart: http://diveintohtml5.info/video.html#what-works
To convert mp4 into webm/ogg format I recommend Firefogg
As for IE 8, it doesn't support the <video> tag, so it will fall back to Flash.
This code is invalid and will very probably be the reason it isn't working:
<script videojs.options.flash.swf = "http://theurl.com/video-js/video.js.swf"
If you can provide a link to a page where this isn't working, then I don't mind taking a look at you.
Hope that helps.