Quote:The Firefox web browser will soon block autoplaying media on webpages visited in the web browser more reliable.
Mozilla added options to control HMTL5 video autoplay in 2015 in Firefox and while the functionality worked fine on many sites, it did not work on others.
Work began to improve the functionality, fix bugs and issues. Firefox may soon block autoplaying media with sound by default in the browser similarly to how Google Chrome handles this.
Mozilla Firefox will block autoplaying media in background tabs if the tabs have never been activated by the user. Autoplaying media may be blocked even if the tab is the active one, e.g. when autoplay is disabled in the preferences or if the media is audible and the user has not interacted with the tab.

Full reading: https://www.ghacks.net/2018/09/21/firefox-improved-autoplay-blocking/