Build Identifier: http://hg.mozilla.org/mozilla-central/rev/dc410944aabc Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/16.0 Firefox/16.0a1 ID:20120610030528 No error detected of wrong RegExp arguments. This invite difficulty of the debugging. Steps to Reproduce: 1. Create clean profile 2. Open Error Console 3. Evaluete the following "aaaa".match('//b[@class="powered-by"]/a[contains(@href, "sites.google.com")]') Actual Results: No error detected Expected Results: An error should detect like following Error: invalid range in character class Source file: javascript:%20"aaaa".match('//b[@class="powered-by"]/a[contains(@href,%20"sites.google.com")]') Line: 1

Good find, I guess bug 724748 just hit release.