I have 3 boxes: "Enable JavaScript source maps", "Enable CSS source maps", and "Allow DevTools to load resources, such as source maps, from remote file paths. Disabled by default for security reasons". The first 2 are checked but without the 3rd trying to load source maps doesn't seem to do anything unless I have them locally. It's very possible I'm just testing it wrong, I don't use source maps often. It's also very possible Firefox does something similar and I'm just overlooking the option/behavior there.