Steps to reproduce:
1) Login to Facebook website
2) Find a post in your newsfeed that has an embedded YouTube video.
3) Attempt to play video (the latest one that prompted this came from an Xbox UK post)
4) After 3-5 seconds the tab crashes, stops responding to mouse and keyboard input (doesn't take down the whole browser though as you'd expect)
Your only choice is to close the tab. To avoid this problem I have at present just been clicking the link in the newsfeed item that takes me direct to the video on the YouTube site.