In chrome, go to :
chrome://flags find the setting ‘autoplay’, and set it to “document user activation is required
In firefox, go to :
about:config find the setting media.autoplay.enabled, double click to set to false.
origin - https://www.pipiscrew.com/2018/03/dont-like-videos-autoplaying-on-your-browser/ dont-like-videos-autoplaying-on-your-browser