For Firefox: About:Config setting media.autoplay.enabled to false.
For Chrome: Chrome://flags set autoplay policy to "Document user activation is required".
I know that this breaks animated .gifs in Firefox, though you can get them to animate by viewing the image info (right-click menu). That's rarely a big loss anyway.
For Chrome: Chrome://flags set autoplay policy to "Document user activation is required".
I know that this breaks animated .gifs in Firefox, though you can get them to animate by viewing the image info (right-click menu). That's rarely a big loss anyway.