I am using Firefox, Win7, plus I have Flash set up so that it doesn't automatically play video.
When I click on the F icon the > comes up and when I click on that the first frame appears. Unlike with YouTube videos when I click play vimeo vids just sit there and do nothing.
Unfortunately I have forgotten exactly how I stopped Flash from automatically starting up so I can't disable that and check that it hadn't got something to do with it right away. I shall have to have a nose around...