It's a known bug that D.O.p.getOwnPropertyDescriptor might throw when applied to proxies, but it's also the case that it throws when inspecting the prototype chains of wrapped natives. This means that almost every use of D.O.p.getOwnPropertyDescriptor in the debugger has to be wrapped in a little try/catch clause with a comment about bug 560072. It's kind of wacky that a function whose job is to inspect properties is unable to inspect properties. For Object.getOwnPropertyDescriptor, there's a public spec that it can't comply with, so for that function to throw makes sense, but the debugger is supposed to help us handle these cases. We can make up variant descriptor types to handle ugly reality. Naturally, this doesn't address the proxy issue; that's a separate problem.