Firefox also has a built-in "broken website" reporter in the Help menu, which sends a report to Mozilla. The WebCompat team analyzes those reports and can decid

Firefox also has a built-in "broken website" reporter in the Help menu, which sends a report to Mozilla. The WebCompat team analyzes those reports and can decide to report a Gecko bug if it has a bug, contact the website if they have a bug, or apply a sitepatch. We're also monitoring the broken website reports for regressions from this change in particular. I understand that a rollout makes reproduction harder, and not everyone will be aware of the change. It's a tradeoff when deciding whether to do a rollout or ride the trains normally.