I am running into the same problem, even with the latest Richfaces 3.3.3.
Did you ever work around this problem?
That issue is not the same as this. In order for Firefox3 to be able to cache resources served over SSL the cache-control header *must* specify "public" (see: http://blogs.gnome.org/jamesh/2008/05/01/firefox-ssl/)
I have a CacheControl filter that adds this for all of my other resources and I can see using FF's about:cache that they are cached to disk rather than memory. However this doesn't work for any Richfaces resources as my filter can't reach them to add the header, so they are only cached to memory.
Definitely a Richfaces issue IMO, and would be an easy fix.