1. Does it work in Chrome?
2. Google this -> How do I disable Flash hardware acceleration?
There can be other causes such as a machine with 1GB RAM but I'm taking your word it's not some old beast that we can't expect to keep up and that you are sure there are no pests or torrents operating here.
Windows Vista Ser Pack 2
The playing of any video has become intermittent.
I have F'fox 24 set at default.
The Adobe Flash Player 11.6 has been updated.
I've reduced the quality of the video to 144, to no avail.
Any suggestions please?