Barring access to Netscape, a step better

The field is User-Agent. However, blocking access to users of Navigator isn't a particularly useful thing to do. If you must do something, why not modify your GET handler to add a header to the start of all html pages informing people of the problem, and suggesting alternatives.

Great idea! I'm sure there is a cyberpunk on this list willing to write a patch to NCSA HTTPd to get the job done, in a configurable manor of course so that a template.html would be 'inserted' at the top of every document sent out to the specified browser. Any takers?