The browser.cache.memory.capacity setting!
Altering this value is a classic engineering trade-off between speed and resource contention. Browser.cache.memory.capacity
Why it exists: Pulling data from RAM is significantly faster than pulling it from your hard drive or re-downloading it from the internet. The browser
serves as a critical lever for performance tuning. This setting determines the maximum amount of Random Access Memory (RAM) the browser allocates to store decoded images, scripts, and objects from recently visited websites. The Mechanics of Memory Caching Browser.cache.memory.capacity
Enter.
A common misconception among novice tuners is that setting browser.cache.memory.capacity to 999999999 (roughly 1 TB) will make Firefox fly. It will not. Here is why: