The secure contextness of dedicated workers should take the ancestors of that worker's document into account. See the test "HTTPS worker from HTTPS subframe" in http://w3c-test.org/secure-contexts/basic-dedicated-worker.html. https://bugs.chromium.org/p/chromium/issues/detail?id=780031 is a related Chromium bug, Firefox gets this right.
<rdar://problem/35275235>