That's interesting.
When I checked there was a signon3.txt. After uninstalling AND deleting the profile folder no such file was recreated. A leftover of 3.0.10? I'm using 3.5b4.
There is, however, a signons.sqlite file.
My passwords were not deleted with the deletion of the Firefox profile folder but for the time being they work.
CCleaner .901 portable continues to be unable to see new cookies, though.