newbie to mac..... question about icons

I needed to load firefox 3.6 because cyber school applications gave a warning on Safari. This was my first install application from the web and it completed with a mounted volume that I figured out how do delete (probably my first mistake). I can see the application in the application folder from Find but the icon I expect to see in the "A"pplications icon looks like a blank page and does nothing when I picked it.

What can I do to put this right?

Thanks in advance.