Originally Posted by facialfreak

First, create the cache on the other drive. Next, in the address bar type in about:config and look for this entry:

browser.cache.disk.parent_directory

Once you find it, double click on it and change the location to the other drive.

Restart FF.

If you don't have that entry, then click on any entry, right click, select New, String. In the first box, enter the entry above, then in the second box, enter the new location. Restart FF.