Accessibility ATbar does not launch: Object doesn't support property or method 'on'

In Moodle 2.6.4 & 2.7 the accessibility ATbar does not launch. Firefox and IE report the following issue:

Object doesn't support property or method 'on'
50bff9805d3122c61e5b9995ba98f2384e10ee81.js, Line: 54, Column: 148

The following URL is called: https://plugins.atbar.org/ftw,resize,fonts,spellng,dictionary,insipio-tts,readability,wordprediction,css,overlay,shortcutkeys,tooltip.js?_=1413296220308

Here is the code which fails:

$lib("a#at-lnk-tts").on("click touchend",function()

{AtKit.call("getSelectedTextInsipioTTS");navigator.userAgent.match(/(iPhone|iPod|iPad)/i)}

)};