Comment 9 for bug 1989195

I've pushed this down rel_3_11. Thanks, Bill and Jane!

I also added a follow-up to add an explicit chrome-headless mode. Interestingly, there are a couple test failures with that mode (on Chromium 90) that pass in Firefox, with elements not becoming clickable or visible in time. However, I decided to weigh getting this in sooner rather than later; perhaps the Chrome e2e tests can be considered experimental for now.