Method 1: Use RAM-only cache
Firefox can be configured to use only RAM as cache storage. Configuration files, bookmarks, extensions etc. will be written to harddisk/SSD as usual. For this
:config in the address bar
set browser.cache.disk.enable to "false" (double click the line)
set browser.cache.memory.enable to "true" (double click the line)
set browser.cache.memory.max_entry_size to the ammount of KB you'd like to spare, to -1 for automatic cache size selection
Main disadvantages of this method are that your tabs won't survive a browser crash, and that you need to configure the settings each user individually. On the other hand on a personal system it probably is the easiest method to implement.