The settings for blocking video autoplay are in the regular Firefox settings page. They no longer need to be manipulated through the about:config page, as was the case when this feature was first launched. Furthermore, the preference that you are modifying is not the correct preference anyway.

Go to the Firefox settings page and select Privacy & Security on the left side. Scroll down to the Permissions section and press the Settings... button next to Autoplay. You can change the default setting and modify any exceptions that have been added.

Firefox provides three options for blocking videos from autoplaying:

• Allow Audio and Video: Videos will not be blocked.
• Block Audio: Only videos with sound will be blocked. Muted videos will start automatically.
• Block Audio and Video: All videos will be blocked.

You can learn more about this Firefox feature from the Allow or block media autoplay in Firefox page.

Hope this helps.

I tried that and it still doesn't work. The videos still autoplay.

Did you check the Autoplay setting in "Tools -> Page Info -> Permissions" for this website ?

Do you see the autoplay icon in the location bar and the play/mute icon on the tab ?

Yes, I've tried that. In this instance, Autoplay is set to default, which is to block autoplaying video and audio. The location bar icon is set to blocked also, and the media still autoplays.

Try this pref setting on the about:config pageṠ:

• media.autoplay.blocking_policy = 2
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

I've just tried that, and restarted FF, and the problem still exists. In Page Info, the source of the video is a blob file. I'm using Privacy mode.