Steps to reproduce:
Start a YT-video with Fx rev/33031c875984 having FlashBlock 1.5.15 installed.
Play the video.
Regression from rev/6c8a909977d3 which plays the video as expected.
Not only with youtube videos and in safe mode (all add-ons disabled) too:
As said above, not flashblock related and not only youtube. Weird that some videos work and other don't.
The first bad revision is:
user: Josh Aas <firstname.lastname@example.org>
date: Mon Aug 29 03:09:22 2011 -0400
summary: Bug 90268: Make content own plugin instances instead of frames. Allows display:none instances and re-parenting instances without stopping them. r=roc
bug 90268 was backed out, fixed by backout: