Different browser means a different client from the same machine

Question

1. If I open a new Tab (or Window) of the same browser I am working on (say Firefox), then it would be considered as the same client by the server.

2. But, if

Answer 1

Technically, this should not be possible. The server identifies clients by setting a cookie on them, and browsers do not share their cookies (they only share them between tabs, that's why you see that different tabs are treated as the same client). You could try identifying by IP address, but then all the clients behind a proxy would erroneoulsy be identified as the same client. Any other way of uniquely identifying a client would involve getting information from the machine (something like the MAC address, for instance) and for security reasons browsers are not allowed to do this.