Netflix Party is a free extension for Chrome:
“Netflix Party allows viewers to synchronize their Netflix accounts into one viewing window through the popular Google browser. Just download and install the extension from the Chrome Web Store and click the “NP” icon on your toolbar while you’re watching Netflix. The app will create a shareable link to the streaming video as well as a group chat bar on the right-hand side of the screen for comments.”
[Netflix Party via Mental Floss]