I regularily use a site that is quite slow and sometimes unreliable. Unfortunately it disallows caching in the browser. Is there a firefox plugin that allows me to cache the content anyway? Ideally, it should try to request a page from the site, but serve me the cached content if the site responds too slowly or is down. It would be really nifty if the plugin would serve me the cached content immediately, load the actual page in the background and replace the content when it's loaded. Of course, one would need to limit this behaviour to specific sites.
In principle one could do most of this also with an external HTTP-proxy. Perhaps there is a proxy that does this? It must work with HTTPS, though - that does complicate things.