PulseAudio alert banner leads to a 404 page
Using Tor Browser 7.0a3, I visited a page that had a video ad (happened to be this one) and got a banner about PulseAudio being required: I clicked the "Learn how" button, and it led me to this page, which is 404 "Page Not Found". https://support.mozilla.org/1/firefox/52.1.0/Linux/en-US/fix-common-audio-and-video-issues (archived copy)
After you have clicked the button once, you can make it appear again by setting the pref
media.decoder-doctor.MediaCannotInitializePulseAudio.button-clicked to false.