great utility - even works again w. YouTube :) Rated 5 out of 5 stars

FB was the last and only XT that was still capable of stopping YT auto-play. Ever since they upgraded to HTML5, FB has become useless for YT (which is where I had almost exclusively been using FB).

(A shame to begin with how YT waste their bandwidth and annoy users - no auto´-play on/off toggle..)

Anyway, Philip, hopefully you feel like updating FB. Raise some funds .. ;)
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03/11/2012: reply to Philip's reply (why can't I reply below your reply here?? Anyway ..):
That's great news, thanks. I realized that YT almost exclusively switched back to HTML4 - I bet 'cause their venture simply didn't work on most comps. They must have underestimated how many idiots out there still surf w. Netscape and Internet Explorer 1 LOL (just kidding - kinda .)

So we're all happy campers, and I edited the comment title and added two **, howz that for a Sunday nite ;)?

This review is for a previous version of the add-on (1.5.15.1.1-signed). 

Flashblock unstable has preliminary support for blocking html5 video.
See: http://flashblock.mozdev.org/installation1.html#unstable