I don't think the cache is disabled.
On the validation request I get "304 Not Modified" response, which implies the file is available in the cache.
Also, I see the same on the Mac, which is a pretty standard installation (ie I haven't done much tweaking there).
I tried to test the example on the extjs website, but there is no Expires header in the response.
Can you check the expiration date for those resources in about:cache?
I don't use cache-control max-age myself, but I've read on the interwebs that it overrides expires. Tests on my system with just the expires headers did bear out what I've posted.
Btw, if you don't have max-age or expires headers, the browsers fall back to default settings. For firefox this is in about:config, the http://kb.mozillazine.org/Browser.ca..._doc_frequency setting, which you have to set to 1. For IE this is on the browser history settings page.
the expiration dates in about:cache match the response headers...
browser.cache.check_doc_frequency is set to 3 (default), but that shouldn't matter as the responses have Expires & Cache-Control headers.
Anyway, it seems I am not going to find out the problem, and I shouldn't bother you anymore as it really seems something strange with my system.
Thanks for your help and if I find a solution after all I will post it here.
One more post to (hopefully) close this issue.
I realized (a bit late) that reload (F5) is not the same as entering the url in the address bar (or accessing the page via a link).
My observations are now as follows
With reload (F5), Firefox validates each file, regardless the expires date.
When browsing to the website (normal situation), Firefox only validates / download files that haven't expired.
And finally (as I started out this thread) with shift-reload (Ctrl+F5), Firefox downloads all files (and some even multiple times).
I have experienced the same problem. My Firefox 3.5 was loading s.gif many dozen times for one single page. Besides stressing the web server, it was also causing ugly rendering of trees, because they were waiting up to several seconds for their s.gifs to arrive.
In my case, the problem was resolved by uninstalling HttpFox Firefox Add-On.