Actually they should be byte-for-byte copies, but generally aren't, since Netflix makes you jump through half a dozen hoops to get the highest quality streams, so pirated copies are actually much better quality than what you can get on Netflix.
I have had the 1080p one for 5 years.
The browser has to decrypt it somewhere along the line to play. Always was interested in tinkering around with it.
For a starting point I'd be going through chromium and checking out how they implement widevine.
For a while now there's been rumors in the torrent scene that a few people have broken it, but keep coy in case it gets patched. Then again it's trivial to screenrecord at the cost of time. Who knows?
Level 3 requires a secure path all the way to the display (so the decryption happens in a Trusted Execution Environment, the keys are stored in a Trusted Platform Module, and HDCP or similar to the display). Level 3 practically only exists on mobile currently, as Intel's SGX (their TEE) is typically disabled by default on what processors do support it.
Does Netflix DRM even "work"? I've never personally seriously looked around for how to break it, but I note there are still plenty of people who seem to manage to review Netflix-based shows on YouTube with video clips of sufficient quality [1], and at least some of the reviewers in question I am fairly confident aren't getting any sort of privileged backdoor access or anything.
Is it "anyone can crack with a smidge of effort" or "it's really hard but it spreads once cracked"? I'm not asking for a lot of details of the crack per se, just general details of how successful it can be said to be in practice.
[1] I'm not claiming they aren't necessarily re-re-encoded by the time they get to me, but if they are, I can't tell for sure, so I'm going with "sufficient quality" as a description.