I had flash working fine, but it stopped working consistently a couple days ago for no apparent reason. For example, youtube videos will start to play fine for maybe half a second, then stop.

Sometimes they will play all the way through with no problems.
Sometimes if it didn't start but I drag the slider to somewhere in the middle it will play all the way through.
Sometimes it will crash Firefox suddenly without any warning.

I tried reinstalling libflashplugin-nonfree, no change.
Any ideas?