Video file works when downloaded in IE but not when downloaded in FF

Question

I am constantly being sent QuickTime MOV files from a client via YouSendIt. Whenever I download the file via Firefox, it appears to download fine but it will not play the video. I get the error message "Error -2048: Couldn't open the file because it is not a file that QuickTime understands." Yet whenever I download the exact same file to the exact same desktop and try to open it with the exact same QuickTime player, but using Internet Explorer to click the download link (and handle the downloading, I suppose)... it works fine and the video plays perfectly. WTF?
All other variables are identical. The only difference here is that the file is unusable when downloaded via FireFox yet perfectly fine when downloaded via Internet Explorer. Why? How is this possible?
The only difference I can see on my desktop is that the version of a test video is 39,305,216 bytes when downloaded using FF, yet the exact same file is 39,370,752 bytes when downloaded using IE. I don't know if that's relevant information but how is this even possible since they are both downloads of the exact same file? Shouldn't both browsers neither add nor remove data from the file itself, so it should be the exact same file? Yet it's obviously different in some way, and apparently different in a way that affects the ability of QuickTime to play the file. Why would this be?

Answer 1

If it works in IE but not FF, then it has nothing to do with the mp3s. More likely it's because of the HTML on the page.
To start, page is missing DOCTYPE declaration... a MAJOR problem. The DOCTYPE declares which set of rules the browser will use to display the page. Without it, different browsers go crazy or do not work at all.
http://www.w3schools.com/tags/tag_DOCTYPE.asp
Validate the html code here:
http://validator.w3.org/
You will have to fix all the errors if you want this to work in all browsers.
Best wishes,
Adninjastrator