There is already some options to manage cache, like:
browser.cache.disk.enable
browser.cache.disk_cache_ssl
But they don't seem to affect streaming video caching. In some cases, it would be more optimal to be able to use RAM for storing video cache.
There is also an option browser.privatebrowsing.forceMediaMemoryCache, but it is only for private browsing mode, it whould be nice to have similar option for the normal mode too.