For some reason, Quicktime handles almost every type of movie. I tried changing the plug-in to the WMP one, but it doesn't allow you to do that. I tried installing the Windows Media Player plug-in for Firefox from microsoft.com, but this had no effect. I tried taking away all video playing capability from Quicktime and adding it to WMP, but this too had no effect. I tried removing the automatic file references in Firefox, but this didn't work either.
I can have WMP the program open the file, but how do I get the plug-in to handle it? For some reason Firefox stupidly doesn't allow you to select the plug-in.