FireFox Help. (Moved from Random Thread)

I need a little help. I have been trying for a very long time to add plug-ins to Mozilla FireFox, but have not been able to. When I first started using Mozilla, when I pushed the button to start the download, the plug-in would just be sent to the plug-in folder automatically. But this is no longer the case.

Can someone please tell me how I can get it let me install Plug-ins (Windows Media Player and Shockwave Player) ono Firefox.