Rated 5 out of 5 stars
How can I make a screenshot here? And I have no contact info from you ... so I give you a possible URL here, where you can see the the Button:
It's the smiley. With MX3, the area is just blank.
EDIT: The developer has responded very quickly, see below ... (thank you dkgo)!
Version 7.3 https://addons.mozilla.org/en-US/firefox/addon/mx3/versions/