CCleaner v5.83 'Custom Clean' is reporting something different than previous versions when cleaning Cookies for Firefox.
This is because of the new way that Firefox now handles cookies.
A few users have already noticed this change and asked about it.
Firefox cookies are still being cleaned by CCleaner v5.83, it's just being reported differently by Custom Clean.
Here's an analysis done with CCleaner v5.82, you can see that for Firefox it's finding:- Internet Cache, Cookies, and Session.
Here is the same done straight afterwards with CCleaner v5.83 this time it's finding:- Internet Cache, and Session, but now finding 1 file in 'Site Preferences' instead of 9 'Cookies'.
(Registry Cleaner and Drive Wiper have also swapped places, but that's not relevent to Firefox).
As said above Firefox has been changing the way it handles cookies, and it now stores each one relative to the website that it came from.
It does this using what it calls 'Partition Keys'.
The 9 cookies found by CCleaner v5.82 are now actually being stored in one file in the Site Preferences, and so CCleaner v5.83 is simply reflecting that change and lists them as that one 'Site Preferences' file where they are now kept.
If you look at the file found under 'Site Preferences' for the analysis above it does indeed contain references to 9 Partion Keys which is the new way that Firefox handles cookies.
To check it even further I let CCleaner v5.83 delete the Firefox 'Site Preference', and then ran a new analysis with CCleaner v5.82.
NO Firefox cookies were found, showing that they had been removed CCleaner v 5.83 deleting the 'Site Preference' file.
CCleaner v5.83 is still deleting Firefox cookies - it's just listing that cleaning differently, because Firefox has changed how/where it stores cookies.
PS. You may also notice that the partitioned Firefox cookies are no longer listed as 'Cookies on computer' in Options>Cookies, that's because they are now in Firefox's 'Cookie Jars' referenced by that 'Site Preference' file.
PPS. If you want to know more about how and why Firefox has changed the way it handles cookies:
https://blog.mozilla.org/security/2021/02/23/total-cookie-protection/
ADDITIONAL INFORMATION:
I have noticed that there is still an occasional cookie found by CCleaner v5.83 in 'Firefox - Cookies'.
This appears to be a cookie from Firefox itself, which would explain why it's not tied to a specific website like the others.