I’m not sure if I’d ever need to use this trick, but it’s still an interesting trick, none the less …
Mozilla has been testing so called stub installers for some time now. What this means basically is that you download a setup for the browser that is less than 300 Kilobyte in size. This is far less than the usual 22 or so Megabytes that users need to download.
There are a couple of limitations though that need to be mentioned. First, stub installers are only provided for Windows. If you download the Mac or Linux version, you get the full version download right away.
While you download 300 Kilobytes initially, Firefox needs to download the rest during installation, which means that an Internet connection is required to install the web browser this way.
The net downloader is only offered on the main Firefox download page. If you visit it and click on Windows, you download Firefox Setup Stub 22.0.exe.
Firefox offline installer
The main problem with this installer is that you need an Internet connection to install it on a PC. While that should not be an issue most of the time, it may be problematic sometimes.
To download the full installer that was offered on this page before, click on Systems & Languages below the big Windows download button, or visit this page directly.
Here you find a listing of all localized versions of the web browser for all supported desktop operating systems. Simply scroll down until you find your language listed here and click on the download button in the Windows column to download the offline installer.
You can use it to install Firefox on systems without Internet connection, or for distribution purposes if you want to install it on multiple systems. With the web installer, you would have to download the browser multiple times (for each system once) which may waste a lot of bandwidth and time.
You can alternatively download the latest full version of the web browser from the official ftp server, or download sites such as Softpedia or Major Geeks.
You are probably wondering why Mozilla implemented the change. This is a good question and there are a couple of answers for that. One comes from statistics that Mozilla published in 2007. According to those statistics, only 57% of Firefox users installed the browser, which means that 43% either did not download the browser fully, did not install it at all, or experienced issues during installation.
It is very likely that this is less of an issue today where more and more users got access to faster Internet connections.
The second improvement is that the web installer will always download the latest version of the web browser. If you are downloading an offline installer, you may need to update the browser manually, which involves downloading data again, after installation.
You have options to download the web installer or the full installer. The only thing that may change for you is that you need to open a different page to download the offline installer. (via Sören)