Try the sign-up form at bottom of this page: http://thermorobotics.com/web/index2.html Try it with no form data and also with invalid email input format..(example abc, abc@, abc@com, etc. Try with valid inputs as well. "No form input data" is caught by jquery on same page Invalid email format is caught by the php page to which the field data is POSTed via ajax. Works perfectly in Chrome and Internet Explorer. It works perfectly even on Firefox on Android. Fails in Firefox..on Windows 7 Professional