Ccleaner cleans, but files regenerate. Fix?

CCleaner for Windows
1

Despite warnings from various Mozillans, I've used Ccleaner Free for years and never a problem with either Firefox or Thunderbird. However, I've noticed something that perhaps the brain trust here can explain to me.

I always run Ccleaner a couple of times before doing a system backup, figuring, "Why back up all that superfluous stuff?" This has seemed to work out fine, but I noticed something a bit strange today. Ccleaner seems to delete a lot of Firefox 'background' stuff, like thumbnails and URL caches. Run it a second time and, sure enough, all that stuff seems to have been deleted. BUT... even after running Ccleaner multiple times, if I do a system restart and then re-run Ccleaner, all that Firefox trivia is back. However, the Windows-default Edge browser seems to remain cleaned through a restart. Can someone here offer a simple (for me!) explanation of what's happening and why? Many thanks.

2

Do you have your Firefox synced to a Firefox account?

Syncing saves all that kind of stuff in the cloud and then sends it down to your devices that don't already have it on them.

So if you have any browser synced then CCleaner can clear the files from your device - and the syncying will just put them back again.

See the link in my signature below this post for a longer explantion of why some files will come straignt back after cleaning and how you can stop some of it happening.