Hi jiembe, do you mean the cookies.sqlite database file? I suppose it is retained for efficiency. Are you concerned that someone could perform a data recovery on the file to extract the cookies it used to contain?

Maybe you're referring to some other files. Could you describe them in more detail?

I assume that you are referring to a report from CCleaner about these cookie files?

Firefox uses one cookies.sqlite file to store the cookies like posted above and doesn't have separate file like MS browser might use, but there are other types of storage that CCleaner might place under cookies that are causing the confusion.

I get this report from CCleaner

I don't know what "0 Ko" is meant to mean. And these cookies are removed if you delete the cookies.sqllite file and then have CCleaner scan again? Or are you letting CCleaner delete whatever it wants, not specific to a particular file?

CCleaner counts data related to secure connections in the SiteSecurityServiceState.txt as "cookies" and Firefox does not. See: https://support.mozilla.org/questions/1213050

The content of SiteSecurityServiceState.txt is not referenced in the CCleaner list above. I haven't try delete the cookies.sqllite file since I have some cookies I had accepted as permanent. So I used instead CCleaner to clear those "cookies" and the time of the 'last modified file date' of cookies.sqllite haven't change.

This could be about local storage as saved in the storage/default folder in the profile folder. The browser-extension-data is where extensions store its data.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox