How Do I Stop Autoplay in Firefox?

In old versions of Firefox, preventing videos from autoplaying required an extension such as the now-defunct Flashblock. More recent versions of the browser have an "Ask to Activate" feature for plugins, which stops Flash videos from loading automatically -- and since Firefox 30, the browser defaults to disabling plugins until needed. "Ask to Activate" does not apply to HTML5 videos, but you can stop these unwanted clips from playing by also turning off "media.autoplay.enabled" on the about:config page.

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Blocked plugins display a gray box with an activation link.
credit: Image courtesy of Mozilla

Step

Open the Firefox menu and click "Add-ons" to open the Add-ons Manager.

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Run the Add-ons Manager.
credit: Image courtesy of Mozilla
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Enable "Ask to Activate."
credit: Image courtesy of Mozilla

Step

Switch to the Plugins tab and scroll down to Shockwave Flash. Open the drop-down menu for Flash and choose "Ask to Activate." If you have Silverlight installed, set it to "Ask to Activate" as well.

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Visit about:config.
credit: Image courtesy of Mozilla

Step

Enter "about:config" without quotation marks in the address bar and press "Enter." On the warning page, click "I'll be careful, I promise!" to access Firefox's hidden settings.

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Change the autoplay setting.
credit: Image courtesy of Mozilla

Step

Search for "autoplay" on the config page, and double-click "media.autoplay.enabled" to set its value to "false." This option stops embedded HTML5 videos from playing automatically, but does not block videos you browse to manually, such as those on YouTube.

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Activate plugins on demand.
credit: Image courtesy of Mozilla

Step

Click on a Flash or Silverlight video to activate a plugin when necessary. After clicking the video, choose "Allow Now" to run the plugin once. To let the current website use the plugin at any time, choose "Allow and Remember" instead.