In the PR at https://github.com/web-platform-tests/wpt/pull/13480 there was a stability test error on Firefox that had a line like so: JavaScript error: tools/wptrunner/wptrunner/executors/executormarionette.py, line 70: TypeError: window.win.timeout is not a function This looked suspiciously like an internal race where remote code was trying to do something in a global that was not fully loaded so I hit the Travis CI button to re-run the stability test. The stability test than passed with flying colors. I'm filing this bug and hitting the merge button on that PR.