I've had a terrible time with hard drive fragmentation, and Firefox eliminated the size of its cache-size adjustment. Out of the box, the cache is 1 gigabyte!! (Allegedly, you can go into about:config and reduce that to 250 MB.) After a couple of hours of browsing, I've been getting 4000 fragmented files and 20,000 fragments. C'mon Firefox; have a heart.

But after clicking Clear Cache, the number of fragmented files drops to 200!

This Clear Cache add-on gives you a choice between clicking and getting a "notification" pop-up to confirm that the cache was cleared, or clicking and getting no notification. I think you need a notification to confirm the action occurred. But there should be an option to have the pop-up disappear after a few seconds, instead of requiring the user to click a tiny x in the corner of the notification each time. That would cut the number of clicks necessary by 50%.