browser.cache.memory.capacity is a hidden configuration setting in Firefox that determines the maximum amount of system RAM the browser uses to store recently visited web pages and images. Unlike the standard disk cache, which saves data to your hard drive, the memory cache is much faster but is cleared every time you close the browser. Configuration Values
Capacity gritted his digital teeth. "Purge the oldest data! Dump the cookies from the shopping site! Clear the history thumbnails!" Browser.cache.memory.capacity
In the search bar at the top of the about:config page, type: browser.cache.memory.capacity browser
However, for the power user with 32 GB of RAM, setting this to 262144 (256 MB) can shave milliseconds off every tab switch. For the developer, setting it to 0 can be a lifesaving debugging tool. "Purge the oldest data
Firefox will display a warning: "This might void your warranty!" Click "Accept the Risk and Continue."