True for most. Unless you have a specific bottleneck or benchmark data, -1 is the safest, most intelligent setting.
Scenario: You have 32GB or 64GB of RAM. You typically keep Firefox open for days with 50+ tabs. You frequently revisit complex web applications (Slack, Figma, Gmail).
Outcome: By increasing the memory cache, you allow Firefox to store more pre-rendered versions of these heavy apps. Navigating between tabs becomes instantaneous. Scrolling through a long history within the same tab feels fluid because assets never leave RAM. Browser.cache.memory.capacity
Recommended value: 204800 (200 MB) to 512000 (500 MB). For extreme users with 64GB+ RAM, 1048576 (1 GB) is viable, albeit excessive for most browsing.
Occasionally, users report that Firefox ignores their custom browser.cache.memory.capacity. Check for these common conflicts: True for most
On Linux distributions with limited RAM, you might want to completely bypass memory caching to free RAM for the kernel's filesystem cache. Set to 0 or 8192 (8 MB).
On older systems with very limited RAM (e.g., 2GB or less), Firefox’s automatic cache might still be too aggressive. By setting a fixed, lower value (e.g., 32768 = 32 MB), you can force Firefox to use less RAM for caching. The trade-off is potentially slower back/forward navigation. Scenario: You have 32GB or 64GB of RAM
Currently, browser.cache.memory.capacity is a static, hidden preference. Users don’t know the optimal value for their system; too low hurts performance, too high wastes RAM. Web apps and images compete for memory without intelligent prioritization.