Actually the expected timeout was added by bug 1563766 which switched the web-platform-tests over to the new emulator recently. So whatever happened there it looks like that we can revert this change. Here a new try build: https://treeherder.mozilla.org/#/jobs?repo=try&revision=dc7fbc5907d3e75f3c2c0aeb2cbcf97106e01a39
Bug 1560033 Comment 12 Edit History
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Actually the expected timeout was added by bug 1563766 which switched the web-platform-tests over to the new emulator recently. So whatever happened there it looks like that we can revert this change. Here a new try build: https://treeherder.mozilla.org/#/jobs?repo=try&revision=263053fac0d3bb1e088c1eb168e482bc294c1def