It means I can actually have a full java plugin installation and just activate the applets I know are safe!

I can have my java and eat it, but people can't make it eat me :)

If the developers at mozilla can't verify the security of the applet, how on earth would my grandmother be able to?

Note: This is not an attack against mozilla in particular, almost all vendors does this (e.g. "antivirus: wanna allow suspicious file?" or "browser: invalid certificate". These questions are asked as if everyone is a computer scientist. We developers need to start formulating these questions so they can be answered by a normal person.

Note 2: I guess it's better than doing nothing at all, since it might stop some drive-by attacks.