So how do open source browsers like Chromium and Firefox do this? Surely if they have access to the blackbox, then anyone does? And if they don't, it means you can't watch Netflix on some major browsers.
Widevine is offered with different levels, depending on the length of the secure path. On mainline Linux, there is no secure path to the screen AFAIK, so you can always read the unencrypted video from a recompiled graphics driver, and as such it only is supported in Widevine's lowest level.
You can also find a link to the Chrome extension there. I'm not sure if there's a cat-and-mouse game here -- the first time I tried it, the Firefox extension didn't work. However, it started working a few months later.