When you use a browser and you log on to a web site like answerbank the logon information is stored in a small file called a "cookie".
Most web sites create a cookie when you visit their site, maybe to keep track of how often you visit the site, or what pages you viewed last time.
The web site may also save your name (if it knows it) in a cookie. Next time you visit the site it may say "Welcome back Fred" to give you a warm feeling.
If you decided to delete all your cookies, then all this information is lost, so when you revisit a site like answerbank you have to logon again.
I have not used CCleaner, but I assume when you run it then it deletes all your IE cookies, so you need to log on again if you use IE.
But maybe it does not delete your Firefox cookies, so you dont need to logon.
If you want to delete your Firefox cookies (or other Firefox temporary interent files) you will need to go into the Firefox options and select an option like "Delete Temporary Interent Files" or something like that.
I have not got Firefox to hand so cannot give you the exact steps to take.