Not at the time it was made. This blog post is from December, the slashdot post from February. The feature wasn't even being rolled out until August. We'll see what happens at the next Pwn2Own...

The underlying engineering effort (e10s) was well underway by that point in February.

E10s has been underway for years though.

OS-level sandboxing for the content process is enabled for macOS as of Firefox 52, which is the current release on the Developer Edition (Aurora) channel and will be rolling out to stable come March. It's currently in stable on Windows and Nightly on Linux. Sandboxing for media plugins is already stable on macOS, Windows, and Linux.

Good to know that this is finally there. I would rather use Safari than a browser without OS sandboxing (which is a no go for me personally).