No drop down menu to block autoplay per your directions.
Followed the directions to block videos from autoplaying. There is no drop down menu with that option under the privacy and security settings.
You must have seen some old directions .....
Would you please do this :
Type in the address bar about:config and press Enter (promise to be careful, if asked)
Type in the search bar :
media.autoplay.enabled and set its value to false and : media.block-autoplay-until-in-foreground and set its value to true
Then close and restart Firefox.