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. However, i got working from another source. Here is the direct link to the mega.nz file for those who need to download it. Just run the setup and it will create iso/dmg file on your desktop ready for installation or transfer. Here it is bit. Ly/2sqyxe4 (remove the space between bit and ly) and open the link in your browser to download it.
A DMG file is a mountable disk image used to distribute software to the macOS operating system. The file is typically downloaded from the Internet by a Mac user, then double-clicked to install an application on the computer.
Today, software developers typically build and distribute applications for Mac users as DMG, .APP, or .PKG files. DMG files are especially common since their contents can be verified upon installation to ensure they have not been tampered with and they can also be compressed to reduce the size of the installer.
When a Mac user downloads a DMG file, he can simply double-click it to open it with the DiskImageMounter utility that comes with macOS. When the DMG file is opened, it mounts a virtual disk on the desktop and in an Apple Finder window as if it was a CD or a USB flash drive that was just inserted into the computer.
In the Finder window, the Mac user can double-click the program icon, which is an APP file, to run the app. Or the Mac user can drag the program icon to the 'Applications' folder icon to move it to the 'Applications' directory in macOS.
After the software stored in the DMG file is installed, the DMG file is no longer needed. Therefore, DMG files can be deleted after installing the software.
While DMG files are Mac-specific and not intended for use in Windows, there are several Windows programs that can extract their contents or convert them to other formats. Some programs include 7-Zip, PeaZip, and DMG2IMG.
NOTE: The DMG format replaced the .IMG file format, which was previously used in Mac OS Classic.