The tests: dom/tests/mochitest/localstorage/test_localStorageQuota.html dom/tests/mochitest/localstorage/test_localStorageQuotaPrivateBrowsing.html dom/tests/mochitest/localstorage/test_localStorageQuotaSessionOnly.html dom/tests/mochitest/localstorage/test_localStorageQuotaSessionOnly2.html dom/tests/mochitest/localstorage/test_localStorageReplace.html all cause lots of occurrences of: ASSERTION: XPConnect is being called on a scope without a 'Components' property In general, these assertions appear to all be assertions about accessing a window wrapped by two proxies, and the JS stack is typically like this: 0 doNextTest() ["http://mochi.test:8888/tests/dom/tests/mochitest/localstorage/test_localStorageQuotaSessionOnly2.html":182] this = [object Window @ 0xca41c68 (native @ 0x91ea2d8)] 1 onMessageReceived(event = [object MessageEvent @ 0xba904a8 (native @ 0xc450248)]) ["http://mochi.test:8888/tests/dom/tests/mochitest/localstorage/interOriginTest.js":34] this = [object Window @ 0xca41c68 (native @ 0x91ea2d8)]

Actually, also: dom/tests/mochitest/localstorage/test_removeOwnersAPI.html dom/tests/mochitest/localstorage/test_removeOwnersAPISessionOnly.html dom/tests/mochitest/sessionstorage/test_sessionStorageReplace.html

This assert is long gone. Any remaining assertions should be in their own bug(s).