I'm fixing this as part of
Bug 1545420 Comment 10 Edit History
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So, this code allows an extension to set the two new properties and necko to use them. I was struggling to create a test tho. There is a WIP patch for it, but it actually can never work, because we either need an h2 tunneling proxy or ssltunnel running for toolkit/components/extensions/test/xpcshell tests. Shane?