At last I've found this addon, ACTUALLY stopping YT autoplay. And doing a lot of very useful things more. Rated 5 out of 5 stars
I'm almost running off my feet, being trying to find WORKING add-on which will allow me to stop annoying YT autoplay. No other stuff worked, no f***in stuff at all and I almost felt into despair. Due to unknown reason I tested this addon at the last. And, it's like miracle - after couple of minutes testing I found that this addon WORKS PERFECTLY. Moreover, I was amazed with level of quality of which this program was created (I even can't name it "addon" - this is fully functional program). Seems like google did it by themselves. And of course I was amazed with number of available settings.
My opinion - this addon must be gold standard for all other developers.
Great thanks for all parties involved! U've created BEST thing i ever met at mozilla addon section.