Why does FireFox 3.6.8 not cache static contents from asp.net developer server?

Question

I am working on a asp.net web site, like normal user, we use asp.net developer server during coding and testing. Today, I found the firefox not cache any static file of my s

Answer 1

You need to issue Expires header to make Firefox cache the files.

Otherwise, how do you think it could guess for how long does it need to cache the files?