central-as-beta simulation: https://treeherder.mozilla.org/#/jobs?repo=try&group_state=expanded&selectedTaskRun=DdiAK-jSTsifIfoTaVGj0g-0&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel%2Crunnable&revision=0799f0ae22aa66449b8845124b82a77f8ef2061f&searchStr=browser-chrome

Log: https://treeherder.mozilla.org/logviewer.html#?job_id=303382464&repo=try

17:07:40 INFO - TEST-UNEXPECTED-FAIL | browser/modules/test/browser/browser_UsageTelemetry_urlbar.js | unexpected counts should be zero for FX_URLBAR_SELECTED_RESULT_INDEX at index 1 - 1 == 0 - JS frame :: resource://testing-common/TelemetryTestUtils.jsm :: assertHistogram :: line 297
4290 17:07:40 INFO - TEST-UNEXPECTED-FAIL | browser/modules/test/browser/browser_UsageTelemetry_urlbar.js | expected counts should match for FX_URLBAR_SELECTED_RESULT_INDEX at index 2 - 0 == 1 - JS frame :: resource://testing-common/TelemetryTestUtils.jsm :: assertHistogram :: line 291
4301 17:07:40 INFO - TEST-UNEXPECTED-FAIL | browser/modules/test/browser/browser_UsageTelemetry_urlbar.js | unexpected counts should be zero for FX_URLBAR_SELECTED_RESULT_INDEX_BY_TYPE_2 at index 1 - 1 == 0 - JS frame :: resource://testing-common/TelemetryTestUtils.jsm :: assertKeyedHistogramValue :: line 360
4306 17:07:40 INFO - TEST-UNEXPECTED-FAIL | browser/modules/test/browser/browser_UsageTelemetry_urlbar.js | expected counts should match for FX_URLBAR_SELECTED_RESULT_INDEX_BY_TYPE_2 at index 2 - 0 == 1 - JS frame :: resource://testing-common/TelemetryTestUtils.jsm :: assertKeyedHistogramValue :: line 354

Hmm, this didn't happen on the simulation I ran in bug 1398416 comment 47. Maybe it's intermittent? Shouldn't be though... I'll take a look.

I think it's because the private search result is shown in Nightly but not otherwise. The test is failing because it expects the private search result to be at index 1 and the form history result to be at index 2, but the form history is actually at index 1. My simulation didn't catch it because it was still a Nightly build, so it still had the private search result. The test just needs to get the right index. There's another part of the test that clicks a remote suggestion, but it's not affected because the search happens to match a couple of history results, so the private search result isn't shown even on Nightly.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=b00d802535c1f25a6826460955a89529d0ffefc5

The private search result is shown in Nightly but not otherwise. The test is
failing because it expects the private search result to be at index 1 and the
form history result to be at index 2, but the form history is actually at index

1. The test just needs to get the right index. There's another part of the test
   that clicks a remote suggestion, but it's not affected because the search
   happens to match a couple of history results, so the private search result isn't
   shown even on Nightly.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=772319cbd460e08e056bebd1e87f8255c10205a9

https://treeherder.mozilla.org/#/jobs?repo=try&resultStatus=testfailed%2Cbusted%2Cexception%2Crunnable&revision=0a2a522a5a5d64fa1bd762b819bcf5aa86d12484

Looks like it fixes it, thanks Sebastian.

https://hg.mozilla.org/mozilla-central/rev/e70cfe6e8da9

Verified fixed in yesterday's central-as-beta simulation: https://treeherder.mozilla.org/#/jobs?repo=try&group_state=expanded&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel%2Crunnable&revision=4071359fca65d9841bc50c2481ec9296463fb8a3