all you need to do to move your caches to RAM is: open up
about:config and make a few tweaks.Once you get into
about:config, type browser.cache into the filter bar at the top.Find
browser.cache.disk.enable and set it to false by double clicking on it.You'll then want to set
browser.cache.memory.enable
 to true (mine seemed to already be set as such), and create a new 
preference by right clicking anywhere, hitting New, and choosing 
Integer.Call the preference
browser.cache.memory.capacity and hit OK.In the next window, type in the number of kilobytes you want to assign to the cache (for example, typing
100000 would create a cache of 100,000 kilobytes or 100 megabytes).A value of
-1 will tell Firefox to dynamically determine the cache size depending on how much RAM you have
