Mozilla now offers Firefox with a web installer. It is called stub installer. This means that the user downloads Firefox setup stub instead of the complete offline installer. The initial download is about 300 KB but when you run the web installer, it will start downloading the latest version of Firefox.
The issue with web installer is that it cannot be used to install Firefox on the system where there is no Internet access. If you are a single user, it is beneficial for you to download Firefox stub installer as it will download the latest version of Firefox.
But if you want to install Firefox on multiple computers, it is probably wise to download an offline installer. This will save you a lot of bandwidth as the setup will not be downloaded again and again as in case of stub installer.
There are two ways to download the latest Firefox complete offline installer. One is using the official Mozilla FTP servers and second is to use the Mozilla’s website.
Downloading offline installer using FTP
The official FTP location of Firefox can be accessed here: ftp.mozilla.org/pub/mozilla.org/firefox/
You will need to go to the releases directory to get the latest stable release of Firefox. You will find all versions of Firefox from the beginning including the stable and beta versions. Each version has its own directory. You will need to go to the directory of latest version of Firefox.
To recognize the latest version, you can scroll to the end of the list and see which version number doesn’t have a letter ‘b’ in its name. For example, right now the latest release of Firefox is Firefox 22. So you will need to go to 22.0 directory.
If you want to download Firefox for Windows, you can go to win32 directory and download Firefox offline installer in the appropriate language as specified by each directory. Likewise, for Linux, you can go to linux x86_64 and for Mac OSX, you can go to the mac directory.
Downloading Firefox using Mozilla.org
The second method is easier than the first one. First go to firefox.com and instead of clicking the download button, click “Systems & languages” link just below the download button. This will open another webpage listing down all the languages and their corresponding Firefox downloads for each Operating System including Windows, Mac OS and Linux.
Just find your language and click on the corresponding Download button. This will download Firefox offline installer instead of the stub installer.