Unfriendfinder isn't available anymore. Quotation from their page:
> The social network asked the removal of the extension because it
> violates its terms.
> Specifically, Unfriend Finder injects unauthorized code into the
> social networks's source code in order to alter the way that the
> webpages are rendered in users browsers
> It adds unauthorized links to users' bookmark sections;
> And posts unauthorized notifications regarding which users have
> "unfriended" the user or "ignored" his or her friend requests.
>
> I cannot enforce this and will cease the developement of this Extension.
> Unfriend Finder has been around for 3 years, and many of you enjoyed
> this, but it cannot go further.
>
> Thank you for your support.
The first paragraph is the also reason why McAfee warned you: code
injection to alter the default behaviour of pages in a manner that users
cannot control.
A problem of UFF, not GM. It seems like in this case, UFF abused the
power of GM scripts to perform unauthorized actions.
Chris