In testing, permissions are granted for a variety of different URIs, with varying schema, and ports. The permission database before bug 1165263 lands did not care about port and scheme, while after it lands it will. This means that permissions databases for testing generated with an old schema will not upgrade correctly into the new schema. Currently, tests are run with fresh profiles, and so this should not be a problem. However, for correctness, it may make sense to nuke the moz_hosts database in mozprofile if an old database schema is found.
You might also stumble across weird legacy stuff like "file://".
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