Recent versions of Firefox come with Electrolysis, or "e10s" enabled, allowing the browser to launch tabs and add-ons in separate processes. What Firefox doesn't come with (for now at least) is a way to manage this new functionality, though one add-on developer has come to the rescue.
A fellow by the handle "TheLaGmAn" has put together an extension called Task Manager and while it works with e10s disabled, users with the feature activated will see the most benefit.
It's a far cry from Chrome's in-built manager, but it gets the job done. Along with showing memory and processor usage, you can kill misbehaving or frozen process with the press of a button. However, there is a caveat as gHacks' Martin Brinkmann notes — this only works with web pages and not internal processes or add-ons.
Task Manager is rough around the edges, but it's better than nothing. No doubt Mozilla will get around to implementing a more powerful native option, but this should tide you over until it arrives.