From MozillaZine Knowledge Base
When a page is loaded, it can be cached so it doesn't need to be rerendered to be redisplayed. For e-mail and news, messages and attachments are cached as well. This preference controls whether to use memory to cache decoded images, messages, chrome (application user interface elements), and secure (https) pages. browser.cache.memory.capacity controls the maximum amount of memory to use.
Possible values and their effects
Allow decoded images, chrome, and secure pages to be cached in memory. (Default)
Don't cache decoded images, chrome, and secure pages in memory.
Users who are having problems with memory consumption can try setting the value to false to lower memory consumption. Users who have no problems with memory should leave it at true.
First checked in
Has an effect in