Comments here on User-Agent fail to mention how browsers can be distinguished by the headers they send and the ordering of those headers. For example, the User

Comments here on User-Agent fail to mention how browsers can be distinguished by the headers they send and the ordering of those headers. For example, the User-Agent header might be the 9th header in a Chrome browser while in a Firefox browser it might be the 2nd header. By default, neither Chrome nor Firefox may send exactly the same number of headers.