Parallels automatically starts on ASPX file extension

I went to a website to download a PDF in Firefox 19 in Mac OS X 10.6. Read on, please.

Because of buggy code on the web site, when I click the link of what I think is a PDF and expect Firefox to handle that, instead it downloads a file with an ASPX extension. This causes Mac OS X to run Parallels, which then opened a guest I only use for archive purposes in coherence mode, and run a Visual Studio debugging program. I already have another copy of Windows already open as a guest, but it wants to open a second copy.

I never never ever want Parallels to run based on how Mac OS X handles a Windows file extension, especially buggy garbage on a web site that I don't catch in time. I also do not want Parallels to open a second guest automatically. If I want Parallels to run I will run it and select which guest I want manually.

Not good, people. Not at all. This should not be default behavior.

How do I fix this?