How to Clear Your Cache in Firefox. The more time you spend online, the bigger your cache will get. Each time you visit a Web site, Firefox captures data from that page and stores for the next time you visit that Web site. Instead of allowing your browser to use up a great deal of memory, you can clear your cache periodically in Firefox.
Clear Your Cache in Firefox
Open the Firefox browser and navigate to the Tools menu (for Windows users) or the Firefox menu (for Mac users).
View the drop down menu display and choose Options (for Windows) or Preferences (for Macs). A new dialog box will appear.
Click the Privacy icon to get to the cache options. Click the 'clear your recent history' link.
Check the "Cache" checkbox and uncheck all others.
Click the "Clear Now" button to clear your cache.