It's usually not a good idea to have third-party applications mess with Firefox files. In any case, you can't delete files while they are in use, and the cache folder and cookie database are in use while Firefox is running.

You can easily clear this data from inside Firefox using the Clear Recent History option. You can find it under the History menu, or you can bring it up with Ctrl+Shift+Del. You can also have Firefox clear things automatically every time you close it.

• Delete browsing, search and download history on Firefox

Other browsers don't seem to have his problem. i enjoy be being able to click on one item and having things cleared without fuss or bother. I'd prefer not to auto delete with each close nor do I want to have to manually hunt down with Ctrl+Shift+Del. I'm aware of those options. I was wondering why firefox still worked that way. Definitely a disadvantage for me using it. reminds me of the story:

A guy goes into a store to buy a suit and the clerk gives him one to try on: Guy, "Hey one sleeve is longer than the other." Clerk says, "Just shift your shoulders like this and it will look fine, see." Guy, "But the pantlegs are uneven." Clerk, "Well, just shift your weight onto one hip and, yes, see it looks fine." Guy, "But the collar rides low on one side." Clerk, "Here, hold that side in place with your chin against your chest like you're holding a violin. Voila!"

These accommodations go on for bit and the guy, somewhat exasperated but worn down, buys the suit. He wears it out of the store and down the street with his chin clamped to his chest, and one leg sort of dragging and his shoulder cocked, etc.

Two doctors walk past him and one says, "Oh that poor fellow," and the other says, "Yes, but he sure had a nice looking suit."

Firefox stores cookies in a database file. Your cleaning application presumably knows that database files can be corrupted (and Firefox probably would crash) if you try to delete that file while in use.

awkward. :(