Why don't I see the same headers coming from Netscape as I do from Internet Explorer?
Request headers are more like hints than required fields. The browsers aren't required to send any headers (although for HTTP POST they must send a content type). Therefore, there's no way to guarantee that different vendors will send the same information. You should write your application so it works even if there are no headers.
Why does Internet Explorer identify itself as Mozilla?
When Internet Explorer first appeared on the scene, the Netscape browser was the most popular browser. Because many Web sites checked for the Netscape browser, Internet Explorer originally identified itself as "Mozilla-compatible" so it could take advantage of all the Netscape-oriented features. Although it is now more popular than Netscape, Internet Explorer still identifies itself as Mozilla compatible. Look for the string MSIE in the User-Agent header and you'll be able to identify Internet Explorer.
I started the Dumper program; why can't my browser access it?
Did you remember to put the :1234 after the hostname? The Dumper program operates on a port number other than 80 (the default HTTP port).
I remembered the :1234 in the URL, so why can I still not access the Dumper program?
Make sure you aren't using a Web proxy from your browser. Some proxies won't access nonstandard ports. If the Dumper program is running on a separate host from your browser, make sure there isn't a firewall between your browser and the program. If you're running this from home, you probably don't have a firewall.