After running C Cleanup I can no longer access two Web sites which are absolutely essential to me: my gmail account and a work-related site which was set as start page in Firefox. (FYI, the login page of gmail is accessible, by my inbox is not.) The problem is only in Firefox and only with these two sites. Every other site I've tried works fine, and I can access all sites in IE.
I've gone so far as to uninstall Firefox and reinstall it, but the same thing happens.
Because of this experience, my impression of C Cleanup is initially VERY negative.