Adobe flash player 10.3 is installed but doesn't appear in plug-ins:what else do I need to do to play videos?

Until a few months ago I was able to play videos in e-mails on my desktop computer, running on windows XP, through Verizon FIOS. Then I kept getting the message that I needed Adobe Flash Player 9.0. I have downloaded the latest version, Adobe Flash Player, several times, getting the message from Adobe that I am now running that program. However, when I try to play a video, I still get the message that the the plug-in isn't installed, and the table of plug-ins doesn't include Adobe Flash Player. Is there something else that must be done to make the (presumably) installed program active? If so, what is it?

Sorry, Firefox 4 is not compatible with Flash for Android.
We're starting work to possibly support Flash for Android in a future version of Firefox. For details, see: