Mozilla has issued Firefox 66 with a big feature addition—an option to prevent Web sites from automatically playing video and audio (see Adam Engst’s “#DeathToAutoPlay—No More Audio and Video That Plays Automatically!,” 6 February 2019). You can choose to block audio autoplay under Preferences > Privacy & Security > Permissions and specify exceptions that you want to let autoplay video. Mozilla notes that the Block Autoplay feature will not stop playing video on some sites (such as social media) where video automatically plays with the sound muted.
Firefox 66 also now implements scroll anchoring to prevent content from jumping as images and ads load at the top of the page, introduces a new way to search through open tabs (accessed via the tab overflow menu that appears when you have a large number of open tabs), improves performance and reduces crash rates by doubling Web content loading processes from 4 to 8, and adds basic support for the Touch Bar on MacBook Pro models. (Free, 64.9 MB, release notes, macOS 10.9+)