jQuery ajax default timeout is unlimited (=0).
Set/Detect Timeout on JQuery AJAX – http://stackoverflow.com/questions/5225597/set-timeout-for-ajax-jquery
http://stackoverflow.com/questions/4148830/anyone-know-the-jquery-default-timeout-value
Browser will have default timeout which controls the request/ response. For IE Refer – http://support.microsoft.com/kb/181050
Online editor to try html/script/css – http://jsfiddle.net/tSW7M/