How do I install applications from a .dmg file? Possible Duplicate:
  How do I install an application from a disk image?  




I just got my first Macbook Pro yesterday and one of the first thing I did was to download and install Mozilla Firefox web browser onto my laptop. After I dragged the firefox icon to the application folder, everything was fine except I was left with a "Firefox 15.0.1.dmg" file that I didn't know what to do. 

I experimented with it and tried ejecting the "disk" and dragging it to trash and emptying it. After I did that the Firefox icon on my dock went black and there was no response when I clicked the FireFox icon on my dock. 

So I had to redownload and reinsintall everything to make it work again. 

Are these dmg files stuck in my computer forever? My download folder is getting unnecessary big
A .dmg file is kind of like an USB stick in a file and can be handled more or less the same way. To install from a .dmg file you usually do the following:


double click the .dmg to make its content available (name will show up in the Finder sidebar), usually a window opens showing the content as well
drag the application from the .dmg window into /Applications to install (may need an administrator password)
wait for the copy process to finish
eject the .dmg (by clicking the eject button in the Sidebar)
delete the .dmg from Downloads