How To Get The New Hangouts In Gmail On Chrome OS X
Recently, my friend Anvita tried sending me a chat message over Google's Hangouts, using the chat box that shows up in Gmail. While I was able to respond to her messages, she always appeared offline to me, and I to her. We noticed that I was still on Google Talk, not Google Hangouts, which ended up being the issue. Should be a simple fix: follow the instructions in this Google support note, click on a "Try the new Hangouts" link, and be done.
But that button didn't appear for me; googling (ha) turned up that a few other people were having the same issue. After some debugging, here's the explanation: the latest versions of chrome disable the NPAPI interface. This should be fine, since the Hangout plugin shouldn't use that deprecated API, but apparently it does. And even though I had the old Google Voice and Video plugin installed, it wasn't being used, since NPAPI was deprecated. I'm pretty sure this is the bug because when I tried Safari, I was prompted to allow the Google Voice and Video plugin, and once I did the "Try the new Hangouts" link showed up and everything worked perfectly.
All hope is not lost: for now, the solution is to go to chrome://flags and enable the "Enable NPAPI" option.
I say for now, because this option will be removed with Chrome 45. Hopefully this helps someone out in the meantime.