To enable it, type about:config into your URL bar, which should bring up a warning. After dismissing it, type plugins.click_to_play into the search bar, then right-click on it and select Toggle. After restarting Firefox, you should see the image above in place of videos.
To do the same thing in Chrome, type chrome://chrome/settings/contentinto your address bar and find the Plug-ins section.
Now, all you have to do is select Click to play. You can also set permissions for specific plug-ins by clicking Manage exceptions.
In Safari, you can download a few extensions to disable autoplay.ClickToPlugin disables all plug-ins from launching content without your permission, and it can replace a lot of media players with HTML5. If you only care about Flash content, you’ll want ClickToFlash instead.
According to Microsoft’s support page, you can use ActiveX filtering to prevent autoplay in IE. Just go to the Tools menu and select Safety, then enable ActiveX Filtering. Now, when you visit a site with ActiveX content, you’ll see a little blue icon in your address bar to let you know it’s being blocked.
To play the blocked media, click on the icon. A menu will pop up, where you can turn off the filter for that site. Once you’re done watching, you can turn it back on by clicking the icon again.