Hi Dori,
You could just look at the hostperm.1 file used to store the blocks on your profile directory, search for wikipedia or wikimedia with a text editor, and remove them that way.
Yes, this is the workaround I did in the end. Not all users may be as "technically savvy" as I though. If wikipedia was not hiding the complete hostname for which it wished to store a cookie this would not be a problem.
Kind regards
JG