Hi Lisq, as the first step, could you try this article:

Allow or block media autoplay in Firefox

Note that Firefox's feature focuses on the initial loading of a page. Sometimes pages will load or start videos in response to a click in the page or scrolling down, and Firefox will no longer be monitoring. For sites like that, you might need to add-on to extend the blocking.

You can look at these prefs on the about:config page to see if these values work for you.

• media.autoplay.default = 1 [0=Allowed, 1=Blocked, 2=Prompt]
• media.autoplay.allow-muted = false
• media.autoplay.enabled.user-gestures-needed = false

For user-gestures-needed you can try false and true to see what works for you.

You can look at this extension. Disable HTML5 Autoplay https://addons.mozilla.org/firefox/addon/disable-autoplay/

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

This may be of help also, the above plus this stopped the damn videos finally. Don't know why this has to be so difficult.

media.autoplay.block-event.enabled;true