Browser Timeouts
It's browser dependent. "By default, Internet Explorer has a KeepAliveTimeout value of one minute and an additional limiting factor (ServerInfoTimeout) of two minutes. Either setting can cause Internet Explorer to reset the socket." - from IE support http://support.microsoft.com/kb/813827
Firefox is around the same value I think as well.
Usually though server timeout are set lower than browser timeouts, but at least you can control that and set it higher.
You'd rather handle the timeout though, so that way you can act upon such an event.See this thread: How to detect timeout on an AJAX (XmlHttpRequest) call in the browser?
You can see the default value in Chrome in this link
int64_t g_used_idle_socket_timeout_s = 300 // 5 minutesIn Chrome, as far as I know, there isn't an easy way (as Firefox do) to change the timeout value.