When you Browse the web your Web Browser caches (stores temporary files) the items you have seen, heard, or downloaded from the Web, including images, sounds and Web pages.
Usually these are temporary files that can make browsing the Web faster because it usually takes your
computer less time to display a Web page when it can call up some of
the page's elements or even the entire page from your local Temporary
Internet Files folder.
If Websites update their code, your browser may still be using some of the old code and some of the new code, which can make the web page display incorrectly. To remedy the problem, clear your cache.
Firefox ver. 3.5 and up - Go to Tools and select Clear Recent History. Optionally you can press control-shift-delete.
Internet Explorer 8 - Go to Tools and click on Delete Browsing History. Optionally you can press control-shift-delete.
Safari - Select the Safari menu and select Empty Cache and then click empty.
Clearing the cache occasionally or regularly can also protect your privacy and free up some space in your computer.