New osx user, need help deleting desktop icon?

[Anthem26]

After downloading and installing firefox on my new macbook, this icon (pictured here: http://imgur.com/Qp11N.png ) would register on the desktop screen and the window for it (pictured here: http://imgur.com/xgYqy.png ) would always pop up everytime I open firefox. I tried dragging the icon into the trash bin, but I would always get "the disk 'firefox' is in use and could not be ejected" popup (pictured here: http://imgur.com/mqTb8.jpg ). How do I go about in deleting this item?

Someone told me to eject the disk img, I tried doing that but the popup "the disk 'firefox' is in use..." would continue to spring up.

From what I've read, I guess the reason the disk img won't eject properly is because I'm running firefox from the disk img, if so, how do I stop that from happening?

 

[MacMini2009]

When you open Firefox, do you get that little window that pops up? There should be a Firefox icon in that window. Open up Finder > Applications. Drag the Firefox icon into Applications. Then try ejecting the dmg. Open up Firefox via the Applications folder and drag Firefox to your dock.

 

[Cboss]

Do exactly what is posted above. I see you have firefox running while you're trying to delete the disk image. You're probably running Firefox directly from the disk image instead of from the application installed on your computer, which is why it's saying the disk is in use.