Could someone be credited with making the first Peer-2-Peer browser?

A browser already operates using peer-to-peer communication. While writing this post my computer is speaking directly with the computer at programmers.stackexchange.com. There’s no central machine in the middle that is handling my connection and the connection to the server here.

How could it send the correct data without it being modified?

You ask the peer for data and it sends that data. It is up to the peer to determine what to give you when you ask. There’s nobody else to get in the way and modify everything.

Would it be faster than normal browsers? (Referring to the way µTorrent works, I find when I use a torrent it’s faster than a web download.)

Torrents are not inherently faster than any other internet communication. All machines connected to the internet have a maximum speed that they can send data at depending on multiple factors (actual internet connection speed, congestion, etc…). As such if you are trying to download a file from a server that has a very poor connection it will go slowly. If you attempt to download the same file from uTorrent and find many peers available for it there will be more bandwidth and thus it will go faster.

Try downloading a file from a provider that you know has plenty of speed available and you will see how fast HTTP can be: http://cachefly.cachefly.net/100mb.test

Can it save on server loads, prevent DDoS, more?

Not really. There’s still a computer sending data and thus said computer can be overloaded with too many requests like any other.