I haven't had a chance to check the PC in question, hopefully today I'll have time to look into this further. This doesn't happen on my PC, using any of the browsers I have (IE and latest Firefox), not sure what version is on my coworker's computer.

I have had issues in the past with FireFox's implementation of the PDF plugin (it will run a print command automatically on opening a document if it appears anywhere in the javascript code, even if it is in an uncalled function, within a false 'if' block, and commented out), but I haven't seen this one before, so I don't know if this problem is Microsoft's fault, or Mozilla's.