Trying to exempt Mozilla cache on Linux

I have hit a configuration wall. Usually I am able to resolve my own problems, but this time it is not working. I have a Linux client with Mozilla, and want to exempt backing up the cache.

I have tried /cache2/, /chache2/entries/, /cache2*, and none of them seem to exempt the Mozilla cache.

Also do these exclusions have to be in place before the backup starts, or can then they be applied while the backup is running?