Screenshots is implemented as a WebExtension. Unfortunately, the WebExtensions framework in Firefox currently appends items to the bottom of the context menu--so you'll notice this with other WebExtensions, too.
There's a bug open to change this behavior: http://bugzil.la/1325758 . If you'd like to hack on some browser JS, I'd be happy to help get you connected with a bug mentor on the addons team :-)
Screenshots is implemented as a WebExtension. Unfortunately, the WebExtensions framework in Firefox currently appends items to the bottom of the context menu--so you'll notice this with other WebExtensions, too.
There's a bug open to change this behavior: http://bugzil.la/1325758 . If you'd like to hack on some browser JS, I'd be happy to help get you connected with a bug mentor on the addons team :-)