I ran Ccleaner yesterday in Custom Clean mode with Cache and Cookies selected for the Firefox application as well all the other browsers. This morning I find that, when I go to various websites I have used previously, I'm not being asked to accept cookies and that I am still logged in to those sites which require it.
Why is this?
If you want to be logged out of sites then in Custom Clean's applications tab tick the "Session" box for Firefox.
Clearing a browsers session closes all the open tabs, logs you out of websites, etc.
ie. Cleaning it removes the traces of what you did in your last browsing session.
If that still doesn't work then you probably have your Firefox synced, and the syncing is restoring them the next time you open Firefox.