Firefox does not use cache on first load and reload

Question

My webserver has a lot of images which will never change. So, I set Expires month forward in such cases:
Expires: Thu, 26 Jan 2012 02:01:25 GMT
Cache-control: public
Enough for IE 9, my server is not disturbed.
But for FF8 and FF9 in following two scenarios my settings are ignored:
1) Close browser. Open browser, look at about:cache - all my files are on place. Open my page - server receives requests for all cached files. And nothing in request allowing server to detect that cache exists.
2) Press Reload button or F5. Again all cached files required. But now requests have
Cache-Control: max-age=0
So, server has some idea about situation and probably can respond with 304.
Only 3) works as I proposed: after 1), open page once more - in the same or another tab. In this case, server receives only requests for files with restricted caching.
Current workaround: I add Last-Modified to response. In this case, I receive If-Modified-Since and can respond with 304. But I have hundreds of small images, so bandwidth for 304 is almost same as for 200 with complete file.
Browser cache settings - all defaults. I use numeric server addresses in current test environment like http://192.168.47.130:27374
I experimented with different modifications of Cache-Control response - without success.
And additional question - how can I make a line break in this editor? If I make a line break and empty line, I get line break and empty line. But if I make a simple line break, I get nothing in resulting text.

Answer 1

Thank you, knorretje. Had no problems with logging on 2003. Lot of lines, but I propose that critical part<br>
0[220f140]: nsHttpChannel::OnCacheEntryAvailable [this=3f6f400 entry=5236740 access=3 status=0]<br>
0[220f140]: nsHttpChannel::Connect [this=3f6f400]<br>
0[220f140]: nsHTTPChannel::CheckCache enter [this=3f6f400 entry=5236740 access=3]<br>
0[220f140]: nsHttpResponseHead::Parse [this=6b113c0]<br>
0[220f140]: nsHttpResponseHead::ParseVersion [version=HTTP/1.1 200 OK]<br>
0[220f140]: Have status line [version=11 status=200 statusText=OK]<br>
0[220f140]: ParseContentType [type=image/gif]<br>
0[220f140]: nsHttpResponseHead::MustValidate ??<br>
0[220f140]: no mandatory validation requirement<br>
0[220f140]: Not validating based on expiration time<br>
0[220f140]: nsHTTPChannel::CheckCache exit [this=3f6f400 doValidation=1]<br>
As I understand, all partial checks say that cache is good. But ending doValidation=1, probably, means that request will be sent. Do not see any reason.