It is not working when open video in new table.

Doesn't perform well enough for initial page load. There will be a brief second or two that the video would still play before it gets replaced by a non-playing video.

the best solution :
https://support.mozilla.org/fr/questions/1238091
in about:config you can set media.autoplay.default to 1 in order to block automatic playback on all pages or set it to 2 to decide on a per domain basis.

Somehow works - but always lets the video play for a couple seconds, then reloads the page and then disables the video on the reloaded page...