Firefox's browser cache is in a constant state of change as you load new pages. I'm not sure it makes sense to worry about defragmenting it. Perhaps just clear it every now and then?

"3-bar" menu button (or Tools menu) > Options > Advanced

On the Network mini-tab > Cached Web Content : "Clear Now"

If you have a large hard drive, this might take a few minutes.

You should not use CCleaner to clear any Firefox related files as Firefox can cleanup its own Cache, Cookies and History.

Thank you for your effort ,but none of your comments actually addressed the question/issue.. Does anyone knows what the "vdimqn76.default" actually is? Why there is "cache2" and huge amount of files with lots of numbers/letters in their file names??? Thanks, Mish

vdimqn76.default is the name of that Firefox Profile.

cache2 is the name of the cache folder in recent versions of Firefox. The cache structure is rather complex now in comparison to a few versions in the past.

As James mentioned, Ccleaner shouldn't be used to clear the cache folders and files; use the "Clear Recent History" feature in Firefox instead.

http://www.janbambas.cz/mozilla-firefox-new-http-cache-is-live/

Hi mishaaustralia, to answer your other question, "vdimqn76.default" is the semi-randomized name of your Firefox profile.