Firefox has joined Edge and Chrome in blocking the audio component of auto-playing video on web pages.
The feature will be coming with Firefox 66, due on the 19 March 2019 and will block any sound from videos which played before the user interacted with a page. Users will be able to whitelist a site however using an icon in the URL bar, and pages, where users had given a site camera and microphone permission, will be excluded, meaning sites which use VOIP video should not be affected.
Google Chrome introduced auto-play block in April 2018 while Edge followed soon after in June 2018, leaving Firefox as the last major browser to introduce the feature.
Read more about the technical implementation of the feature at Mozilla here.