It would be really nice if the addons/extensions page showed which addons were listed as compatible and which weren't. I might thus make a decision to disable/delete an addon or two that were blocking me from using multiprocess firefox. As it is, I have no idea if my firefox is using multiprocess at all. All I know is that I use a lot of addons and I'm probably not, then, using multiprocess.
You can figure out what add-ons are compatible by cross-referencing http://www.arewee10syet.com/
Edit: The page for the addon has a comment saying it does work with multiprocess, so I just forced it on. I'm on Linux, and I don't know of an about:config key to disable ctrl+q