click me .. demonstrates the browser freezing up for 5+ seconds by executing a 5-second-slow synchronous AJAX call

This is "by design" since Javascript, HTML, and the browser's UI events all execute on the same UI thread. However, I think it would be ideal and appropriate if the browsers sought to isolate the Javascript & HTML thread from the OS UI thread. Being that I believe that this is generally doable, I consider this a bug.

These are the browsers tested to display this behavior:

• Internet Explorer 7
• Firefox 2.0
• Safari 3.1 for Windows

These seem to have it resolved:

• Firefox 3 (rumored; still in beta, haven't tested it for this)
• IE 8 (partially; can update the addressbar or resize/maximize/reposition the window, but not click on the menu nor toolbar nor close the window; also in beta)
• Opera 9.27 (even the HTML is isolated from the script; nice job!)

None of these except for Opera even took the time to change out the document body cursor like I told it to before the AJAX call. What's up with that?

The file on the server looks like this:

<%@Page Language="C#" %>
<%
Response.Cache.SetCacheability(HttpCacheability.NoCache);
System.Threading.Thread.Sleep(int.Parse(Request["delay"]));
Response.Write("OK");
%>

- Jon