CCleaner clearing allowed popup sites in Firefox

It appears that CCleaner is clearing the list of allowed popup sites in Firefox. I'm not sure why there would be any feature in CCleaner to do this. Anyway, it appears that the "Site Preferences" item under Firefox is what causes this... unfortunately, this option does not appear to be documented in your online docs. What else does this feature do?

Yeah it's the Site Preferences item, which caught some of us out of the blue! It's something to untick in CCleaner because it cleans differently now than it did in the past, although with all the posts about cookies not being deleted in some browsers perhaps that's why it works differently now.