It is a bug in the older version of Flash. However, you do not have to upgrade to F9 or better to solve this difficulty.
What you do is uninstall Firefox (that you got from the Fedora repositories) and install the one located here: Newest Firefox
. Making sure you select the proper language and OS type you desire. Once downloaded just follow the directions for installing it either globally (e.g. all users) or just in ~/home.
With the latest version of Firefox installed you can then install the latest versions of your extensions and add-ons as well.
btw, sometimes resetting the content of the browser by depressing the F5 key will help resolve the issue.