Why can't I edit my Firefox cookies in Intego's Washing Machine?

Washing Machine will allow me to delete all of the cookies in Firefox, but will not allow me to edit them. I have tried double clicking, “right” clicking, and using the toolbar, but it will not let me edit them.

This is a recent problem which makes me think it could be a virus, but my virus scans all come up clean.

I’m using a Macbook Pro that is almost four years old.