Hi vjones2, the Firefox installer for Mac uses a .dmg container, but when you install, you actually pull Firefox out of the container into a local folder. (After that, you don't need the .dmg file any more.) Could you take a look at the method in the following article and let us know whether it works: [[How to download and install Firefox on Mac]] Also, don't let go of your old Mac since we may suggest copying some files off of it.