For memory, you can already look at about:memory. For performance, if you are running Nightly, you can use the Gecko profiler that basically tells you everythin

For memory, you can already look at about:memory. For performance, if you are running Nightly, you can use the Gecko profiler that basically tells you everything about what takes time. Note that, by design, the Gecko profiler is activated only on Nightly releases. But yes, both features are rather hardcore. We are working on more user-friendly solutions, too, although I have no idea of the roadmap.