In bug 1522508 I was having issues with getting the tests stable with QuantumBar.
browser/components/extensions/test/browser/browser_ext_omnibox.js would run the first section
testInputEvents, but then randomly hang whilst running the
I found that adding
promise.then(timer.cancel); to cancel the timer if the handleSearch promise was resolved seemed to make things work better.
We should work out why that is, as it doesn't quite make sense. I suspect it might be something to do with how the promises/timers are resolved.