Works some of the time Noté 3 sur 5 étoiles
Stopping autoplay works some of the time. Might be a bug in Firefox itself, as it does crash a lot and for a long time before a crash, or in otherwise poorer performance conditions (like when Firefox gets very slow) plugins generally function more poorly.
Preference for higher resolutions seems to work reliably.
It now also gives an error message "Error: Adblock (or similar extension) is known to interfere with SmartVideo. Please add this url to adblock whitelist" without specifying what URL to add. Adblock DOES have youtube-specific filters active, in Easylist and elsewhere, but I won't disable them at random and without a good reason.