[Dylan16807]

User-Agent: modifying based on this is a Bad Thing

Referer, If-Unmodified-Since: these only decide if you respond or don't or error, they don't generally change a successful transfer

Accept-Language: I was under the impression that this was buggy and not well-supported, but it is a good example in theory

[icebraining]

The response is changed all the type depending on the value of the Cookie header.