I'm a bit confused as to how HTTP headers work and I'm overly confused about the difference between 'if-modified-since' and 'last-modified'. They seem to be generated by the websever in the most part, so is it easy to get a 304 response from the server if you put the right cache headers in? Or would have to code a script in to produce the right responses?
I think 'if-modified-since' is set by browser client based on the cache it has on the user computer, I don't know if you can play around with this value in firefox or ie.