How do I detect what browser (IE, Firefox, Opera) the user is accessing my site with? Examples in Javascript, PHP, ASP, Python, JSP, and any others you can think of would b
If it's for handling the request, look at the User-Agent header on the incoming request.
UPDATE: If it's for reporting, configure your web server to log the User-Agent in the access logs, then run a log analysis tool, e.g., AWStats.
UPDATE 2: FYI, it's usually (not always, usually) a bad idea to change the way you're handling a request based on the User-Agent.