When Confluence is available over HTTPS and clients try to access it with Firefox, the reponse time is very long (7 to 9 seconds instead of 1-2 seconds) because by default Firefox uses no caching mechanism with HTTPS.
A manual configuration involving the "browser.cache.disk_cache_ssl" parameter of Firefox is necessary for people to restore a correct response time. The point is that after this customization ALL web sites using HTTPS are cached, including the sentitive web sites such as bank sites...

As described on the following web site http://blogs.gnome.org/jamesh/2008/05/01/firefox-ssl/ this could be avoided by making Confluence server send the "Cache-Control: public" response header, thus making the server say that a resource can be stored in the disk cache