Memory Cache is a project that allows you to save a webpage while you're browsing in Firefox as a PDF, and save it to a synchronized folder that can be used ...
Type about:config into the address bar, press Enter, accept the warning, scroll down the alphabetical list to browser.cache.disk.smart_size.enabled and double ...
The answer as to why it's like that is because internally disk cache includes by default memory cache. The result is a slightly irrelevant about:cache page.