Javascript snippet freezes Firefox3.6

Question

This code is freezing Firefox 3.6.

 // Google Code for Converted Users Remarketing List
    function converted_remarketing() {
        window.google_conversion_id = 1018522404;
        window.google_conversion_language = 'en';
        window.google_conversion_format = '3';
        window.google_conversion_color = '666666';
        window.google_conversion_label = 'e9x2CKzhXXXXpNbV5QM';
        window.google_conversion_value = 0;
        var a = document.createElement('script');
        a.type = 'text/javascript';
        a.async = true;
        a.src = 'https://www.googleadservices.com/pagead/conversion.js';
        var b = document.getElementsByTagName('script')[0];
        b.parentNode.insertBefore(a, b);
    }

converted_remarketing();

Example page: http://jsfiddle.net/LLSu4/11/show/

Looks like it has something to do with the script insertion. The funny thing is that I copied the insertion snippet from Google Analytics code that works flawlessly.

So the question is, why is it freezing Firefox 3.6 and why it doesn't freeze Firefox3.6 when a very similar code is ran to load Google Analytics script ga.js?