Move/set Firefox cache location

You can do this by creating a new hidden preference.

Type about:config into the location bar and press enter

Accept the warning message that appears, you will be taken to a list of preferences

Right-click somewhere in the list and select "New > String"

For the name of the preference type browser.cache.disk.parent_directory

For its value type the path to where you want to store the cache, for example d:\fftemp

Next locate the preference browser.cache.disk.enable, it must be set to true, if it is not, double-click on it to change its value

Set the size of the cache to something like 32000 to 512000 by setting browser.cache.disk.capacity (32-512MB)

For more information on this see: https://support.mozilla.org/en-US/questions/768867