The cache size usually ends up around 350 MB, unless you have very little free disk space. I suggest you start over: # Type ''about:config'' into the address bar and press Enter. # Press the big button to bypass the warning. # In the search box, type ''browser.cache.'' # In the search results, right-click each entry with the status "user set" and choose '''Reset'''. # Type ''about:cache'' into the address bar and press Enter. Under the "Disk cache device" category, note the value of the '''Cache Directory'''. Open that folder in Windows Explorer. # Exit Firefox (click the Firefox button in the top left corner, then choose Exit). # Delete the cache folder you opened earlier. # Restart Firefox. ---- At that point, your cache size should be set to something more sensible. Note that under [[Advanced settings for accessibility, browsing, system defaults, network, updates, and encryption|Options - Advanced - Network]], the number box shows the maximum cache size, while the text above it shows how much is currently stored.<br> If you still need to override the automatic size, then normally all you need to do is check "Override automatic cache management", specify a custom size below, then click the OK button.<br> Doing so would save the first preference as ''browser.cache.disk.smart_size.enabled'' with a value of '''false''', and the second as ''browser.cache.disk.capacity'' with a value in [http://en.wikipedia.org/wiki/Kibibyte kibibytes]. To avoid unintended effects, it's best to avoid modifying about:config preferences (at least in this case). ---- If your preferences are lost after restarting Firefox, see the following article: * [[How to fix preferences that won't save]]