User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:74.0) Gecko/20100101 Firefox/74.0

Steps to reproduce:

I suspect this happens on all test runs in the 18.04 image. e.g. https://firefoxci.taskcluster-artifacts.net/cGmS9xPdRVue9UymmXE-UA/0/public/logs/live_backing.log

Actual results:

Got the error message.

Expected results:

Didn't get it.

This is annoying for Pernosco because we see the "error" bit as something relevant to us when in fact it's just useless noise. I've hacked around this on our end for now but it'd be good to get it cleaned up.

This should block bug 1565332.

I'd like to take a look at this before I go on parental leave, but the MDC1 outage is affecting my ability to push to try.

try push: https://treeherder.mozilla.org/#/jobs?repo=try&group_state=expanded&tier=1%2C2%2C3&revision=fbf13a16b249adc913b3d607779396ab09e7fbc1

This seems to be a deeper problem to fix than just setting the environment variable, since doing so will break the baseline I'm using for some reason (mochitest-plain-e10s-1).