You are running Firefox on a legacy system with 4GB of RAM. You also run a Virtual Machine, Adobe Photoshop, or a local development server (Docker, Node). Every megabyte matters.
: If it doesn't exist, you can create it by right-clicking in the window, selecting New > Integer , and naming it browser.cache.memory.capacity . Browser.cache.memory.capacity
Unlike the (which stores website data on the hard drive for long-term storage), the Memory Cache stores recently accessed web data in the computer’s RAM. You are running Firefox on a legacy system with 4GB of RAM