I like to have a separate partition to keep things like temporary internet files in, in order to reduce the fragmentation on my primary partition. The downside to this is that CCleaner seems to "miss" the clearing the FF cache, since I suppose it is expecting to find the cache folder in the standard location. I think it'd be a great addition to have CCleaner check FF to see where the cache folder is actually kept, then nuke that cache .
Keep up the good work though, I really love CCleaner!
BTW, I also have my IE cache folder on this partition (non standard location), but CCleaner seems to find and clear it just fine.