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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

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marked as duplicate by Gerry, jmlumpkin, Jason Salaz Sep 21 '12 at 20:29

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

up vote 8 down vote accepted

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
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