Why doesn't my expires headers make my files stay in cache?

I开发者_Python百科'm using valid expires and no-cache headers for my static files and they stay cached for as long as I keep browsing, but when I close my browser and use it back after a while I see the static files loading again, even when not refreshing with ctrl (+ shift) + r

I'm using Firefox, cache size set to 250MB and I don't let it remove any private or cached data.

Headers: Accept-Ranges: bytes Cache-Control: max-age=29030400, public Content-Length: 142061 Content-Type: image/png Date: Tue, 08 Dec 2009 19:18:43 GMT Expires: Tue, 09 Nov 2010 19:18:43 GMT Last-Modified: Sun, 18 Jan 2009 18:33:48 GMT Server: Apache/2.2.14 (EL)

Which version of Firefox? Is the server sending Etags for the static files? You can view details about Firefox cache by going to the address about:cache and poking around. That will give you an idea of what Firefox is caching.

Update: After looking at your header tags, it seems as if the max-age value is set to a date that is way in the past and that is overriding the the value being set in the Expires header. See the HTTP 1.1 protocol definition at: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.3.

If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header, even if the Expires header is more restrictive. This rule allows an origin server to provide, for a given response, a longer expiration time to an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This might be useful if certain HTTP/1.0 caches improperly calculate ages or expiration times, perhaps due to desynchronized clocks.

You will have to modify your Cache-Control header being sent by the server.