https://support.mozilla.org/en-US/kb/block-autoplay
Som sagt, som man normalt ska göra fungerar inte!
Från länken ovanför :
Fx69Permissions-Autoplay
Find Autoplay and click the Settings… button.
Fx71Permissions-AutoplaySettings
The Settings - Autoplay list will open.
(Nej)
You can use the Search field to find a specific site.
(Den hittar ingen sida alls)
To add a website with a different autoplay setting, you must visit the website and use the Site Information panel, as described on Site settings above.
(Fungerar inte. Den hittar inte någon sida alls)
You can use the Status drop-down menu next to a website to change its autoplay setting. (Note: Changing the status to your default setting, the website will be removed from the list after you save the changes.)
Click the Save Changes button to save your changes.
(Finns inget att spara!)
Vart hittar jag autoplay inställningen i About config?