"paste" is not enabled for non-trusted scripts on FF 41+. A extensions' scripts can use "paste" since they are trusted scripts; but a webpage's script cannot.

I believe that footnote is a doc error, since copy/cut are enabled w/o user.js override on FF 41+.

I don't know if there is any current plans to make "paste" available for all scripts - I don't think there would be because of the obvious concerns.