:sphilp asked how long this would increase run time.
I happen to be running
test-windows10-64-ux/opt-raptor-tp6-1-firefox-e10s locally and it takes 19 minutes to run on the reference laptop.
The browser is loaded 4 times for this test, once for each site, so adding 60 seconds to each browser startup would bring total test time to 23 minutes, if I'm not mistaken.
Maybe an additional 30 seconds is sufficient to reduce the noise?
I was told that the openh264 codec is downloaded after a minute, this could be introducing some noise.