If using Firefox and Firebug is disabled, then the object "console" is undefined. wdp-ajax-comments doesn't account for this. To fix this scenario, insert the following in ajax-comments.js at line 12, immediately before the "console.log" line:
if( typeof( console ) != 'undefined' )
This will cause Firefox (without Firebug) to resume processing JavaScript code after ajax-comments.js, instead of crashing the interpreter.