This happens for me sometimes too at work. I believe it's due to local caching, or caching performed by your ISP. (AOL caches almost everything, and some other ISPs do as well.)

I don't know if this is Francois' problem but it does affect lots of people.

Most companies will have something called a proxy server that will also cache external web sites. So your browser thinks its getting a fresh copy (ie not from the local cache) but instead is getting a stale copy from the proxy.

There is no way that I know of to force your proxy to go out and fetch the latest version (or even not to cache the page at all). Sometimes hitting refresh several times works. (there are some ways of setting up your website to avoid this problem, but some proxy servers can and do ignore these settings).

I do not recommend bypassing your companies proxy server BTW, as this has been known to get people fired.

I suspect it is a bug. There are some pages that simply will not load until you delete the local cache. You can improve the performance though:

Type "about:config" in the address bar.

Search for the string "browser.cache.check_doc_frequency", and set the value to "3".

You can search the web for more information about this string.