I have some Ajax stuff that will just error from time to time due to database timeouts, etc. I need to turn off the dialog that comes up that says there was an error and to turn on debugging. It just freaks end users out... It would be nice if such errors were just reported in firebug with no "Click OK" popup dialog! Maybe a try/catch is in order??
This depends on the code you are using.
If you are doing ajax calls then you probably have an alert() inside the function that gives this alert when a certain case is matched.