Sorry I have had to mark this as unsolved again, as it has started happening again.
I looked at Task Manager and there are TWO adobe flash processes running. I don't understand why that is.
And the bigger one is sometimes even overtaking Firefox itself as the number one resource user.
I have not installed another version BTW. I still have version 11.3.300.214 Beta 1 (Non-IE) 64-bit.
I have found this page Adobe Forums: Flash Player 11.3.300.257 Keeps Crashing On Mozilla Firefox 13
...that shows lots of other people have problems with it. I don't fully inderstand what the Adobe Employee is saying, but from what I can see he is making people jump through an awful lot of hoops - and none are working!
Some of the troubleshooting involves having to register at their site and submit bug reports, but they don't tell you how. They are also suggesting using a different browser. I can understand this from a diagnostic POV but not permanently. That's unacceptable!
It seems to be suggested that the problem exists because there are TWO Flash players on people's systems. But they tell you if you uninstall one, it will uninstall both!!
I'm really confused and fed up!
Any ideas please?
thanks a lot