A browser cache serves for acceleration of browser work, reduces network load and quantity of inquiries to internet site, which increases its performance. When you open one page in browser then another and then return back to the first one then browser will download it from your hard disk, where it was primarily cached. This is performed much faster than getting the same document from the network.
Page viewing is very important to get HTML code and to download from network all accompanying documents like CSS-files, images and the script issued in the form of separated files. Most viruses, network worms and malware-programs execute from temporary files directory, so wrong adjustment of cache work and insufficient anti-virus control may turn temporary internet files into "virus territory." Large cache also negatively affect the work of a browser and PC hard disk subsystem, as a result, internet cache advantages disappear.
The adjustment of internet cache size is possible in Firefox menu Tools - Options - Advanced - Network - Offline Storage. Here it is also possible to limit hard disk space for temporary files' storage or delete them right away ("Clear Now"). If necessary, the present operation can be performed differently: wipe the internet cache directory manually or create file clear_ff_temp.Cmd with the following content: rd /s /q "%userprofile%\Local Settings\Application Data\Mozilla\Firefox\Profiles"
This CMD file will delete all Firefox temporary storage on this computer. It should be performed, for example, before anti-virus scanning along with Windows temporary files folder wiping (C:\Documents and Settings\_USER_NAME_HERE_\Local Settings\Temp), because in this case thousands of odd small files (standart quantity of temporary files of Windows and browser) won't be processed, so it will save you some time. This will also delete viruses and malware if they had already been there.