Open a CMD prompt, and issue the following command:
assoc .tmp
This should (normally) result in the message:
File association not found for extension .tmp
If a file association for .tmp is given, then you can disassociate the .tmp extension by issuing this command:
assoc .tmp=
I'm just suggesting this as a first / precautionary step. I don't think that the .tmp extension has actually been associated with anything, but it doesn't hurt to check.
I suspect that this may have something to do with bad scripts or applets at some of the sites you're visiting or your browser security settings or a combination of both. Speaking of which, have you installed the JVM on this system? Does the error ever happen when you're not using your browser? If not, I'd be tempted to not sweat it. If you watch carefully, you might notice a correlation between this behavior and a specific Web site or sites. If you post them, other people could go check 'em out to see if they can see evidence of bad execution, though that sort of thing could be pretty hard to track down.
Regards,
Jim