mass unfollow extension.
Haven't packed it or anything yet so you'll have to follow the unpacked extension method.
Because of the way the content-script functions you'll have to reload the twitter.com/*/following page once to see the button in the top right corner.
It will also persist in normal operations until a reload not on that page is performed. Clicking it outside of the intended page only has the effect of clicking any unfollow buttons outside of that page.