When I installed version 10 of the Flash Player on my macbook pro everything seemed to work ok. I use WordPress and at the time v10 of flash broke the multi-upload feature. Because of this I decided to back off to v9. All seemed well except that I noticed that some flash based sites didn’t view at all. I assumed that it was because they were published for flash 10. Later on I gave in and installed the v10 player again. I noticed that some sites still didn’t work. I knew the problem wasn’t the plugin itself because everything worked fine in Safari. Finally I trashed Firefox and reinstalled it. This didn’t seem to help. I figured there were probably some config files left behind so I trashed it again after enabling AppTrap. This allowed me to trash all config and support files for Firefox at the same time that I trashed the application itself. I then reinstalled and everything has been working every since then. I hope you find this post helpful if you run into the same problem.