browser.cache.memory.capacity is a scalpel, not a sledgehammer. Use it precisely, and Firefox will reward you with unparalleled responsiveness. Use it carelessly, and you'll simply waste precious RAM.
Here's some information on the browser.cache.memory.capacity parameter: Browser.cache.memory.capacity
The memory cache stores web resources—such as images, scripts, CSS files, and HTML pages—directly in your computer’s RAM (Random Access Memory). Because RAM is orders of magnitude faster than a hard drive or even an NVMe SSD, retrieving a cached resource from memory allows pages to reload almost instantly, especially when using the back/forward buttons or revisiting a page in the same session. browser
: Double-click the preference to change its value. Deciphering the Values: What Numbers Should You Use? Here's some information on the browser
: Sets a fixed limit (e.g., 131,072 KB = 128 MB). Common Use Cases