So what is NSS? It stands for Network Security Services which is a joint effort of Mozilla, Google and RedHat. They're nothing you'd normally interact with as a typical end user, but they're helpful for developers building applications where security is paramount. (And protecting the streams of intellectual property provided by movie studios and television networks is a pretty high priority for the folks at Netflix.) The current stable version of Ubuntu (14.04) is running a slightly older version of the plug in, but it should make its way to the OS soon via a security update. And the next version, due in October, should carry the newer NSS when it ships.
Crafty Linux users have been able to work around Netflix's restrictions with hacks, but no average person wants to tinker with their browser's user-agent. With the shift to the new HTML5 player, the world's most popular streaming movie service will officially supported on desktop versions of Linux. Of course, Netflix already works with plenty of Linux-based devices (see Android, Roku, Chrome OS, etc...), so this really shouldn't come as a huge surprise.
Update: It's important to note: Linux will support Netflix, not the other way around (for now). While the streaming service may soon work on your Ubuntu box, it's technically still not a supported platform. That means if something goes wrong, don't expect a customer service rep to sit on the phone while you struggle to kick off your Firefly marathon.