[rv11]

I don't think they use any specific plugin, but use webRTC instead for hangouts

[TD-Linux]

Hangouts uses a bunch of non-standard Hangouts-specific APIs in Chrome. Maybe it's be best to call it "Google-RTC".

https://webrtchacks.com/hangout-analysis-philipp-hancke/

In summary, they use weaker encryption than allowed by the spec, nonstandard ICE (firewall hole punching), nonstandard data channels, and an abandoned way to do multistream.

[cpeterso]

Hangouts uses a plugin (NPAPI or ActiveX) in browsers other than Chrome.

[ungzd]

Seems that extension is involved: http://imgur.com/a/HLpLf

[cpeterso]

Hangouts on Chrome uses NaCl for some visual processing (like hats), or at least it used to. So the NaCl code may show up as a plugin process.

https://webrtchacks.com/hangout-analysis-philipp-hancke/