Web caching in general refers to temporarily storing of web pages, images and other web elements on local computer for a faster user experience when these elements are accessed again. Hence all browsers keep cache files which often tend to grow to a large size if not properly cleaned or managed.
For Firefox 5, it is possible to manage the size of cache files manually.
To do this :
1. Select Tools > Options.
2. Go to Network tab and enable the check mark next to Override automatic cache management under the Offline Storage tab.
3. Set the size of Firefox 5 cache as desired (don’t set it too low) and hit Ok.