To find the location of your disk cache, type about:cache in the address bar and press Enter. Note the value of “Cache directory” in the Disk Cache Device section. The Offiline Cache only contains data from those few websites that have specifically asked you to store files on your computer (if any).
i need to backup and restore cache for better protection
You seem to be running Firefox 3.6.28, which is a very old obsolete version that contains numerous security vulnerabilities. Your computer not protected from security threats. Not only that, but the latest version of Firefox has a larger cache by default, and is much better at managing it, both in terms of performance and in avoiding discarding cached files prematurely.
i use a dial up connection and i need to restrict Firefox from deleting its cache because that speed up surfing and i find a program that help me to do this thing ...... how can i backup and restore cache manually without to need to buy the program
Backing up the cache won't accomplish anything apart from wasting your time. If you keep replacing the cache, items that were downloaded into it since your last backup will have to be downloaded again.
If you want to spend less time waiting for things to download: