From MozillaZine Knowledge Base
This article will help you install Firefox on your system. Once Firefox is installed, the Software Update feature provides for automatic download and installation of future Firefox updates (see the linked article for details).
Download the Firefox installer from mozilla.org or go to this page to choose the full installer for your language and OS. System requirements for the current version of Firefox are listed here. If your computer doesn't meet those requirements, you can download a previous Firefox version from the CDN server. System requirements for Firefox 3.6 are listed here.
If you install Firefox on a multi-user system where access privileges are restricted, you must run Firefox as a user with access to that location upon installation so that all initial startup files are generated.
Note: In most cases, you can install a newer version of Firefox over an existing version . If you prefer a clean install, Uninstall your current Firefox version and delete the installation directory before launching the Firefox installer.
Using any browser, download the Firefox setup file to your desktop or other location. After the download is complete, exit Firefox completely (if open). Double-click the downloaded setup file to launch the installer. See the article Installing Firefox on Windows for detailed information, including Standard and Custom setup and screen images.
If you have problems with the Firefox installation, do the following:
First, download the latest release to your home directory with your browser or download manager.
bash$ cd ~ bash$ wget http://download.cdn.mozilla.net/pub/mozilla.org/.../firefox-<version>.tar.gz
Next, extract the contents with an archiving utility such as Ark or tar.
bash$ tar zxf firefox-<version>.tar.gz
Now you must select the installation directory. If you are the only user, the extracted files could stay where they are, but If this is a multi-user system, the firefox directory must be moved to a publicly accessible location such as /usr/local or /opt.
bash$ su <password> bash# mv firefox /usr/local bash# chown -R root:root /usr/local/firefox
The installation is more or less complete, but it's recommended that the firefox script be available somewhere in your path to avoid the inconvenience of having to enter the full path. This can be accomplished by creating a symbolic link in the relative 'bin' directory.
For the personal installation:
bash$ mkdir bin bash$ cd bin bash$ ln -s ../firefox/firefox .
Or the mult-user installation (as root):
bash# cd /usr/local/bin bash# ln -s ../firefox/firefox .
Many Linux distributions already include /usr/local/bin and ~/bin in their global environment variable path, which can easily be verified by running 'firefox' from the shell or the desktop environment's (run) menu. If execution fails (command not found), you can adjust the path by appending "/usr/local/bin:$HOME/bin" to the existing PATH variable in /etc/profile and/or /etc/bashrc.
Mac OS X
Mac OS X system requirements for the current version of Firefox are listed here.
Do not double click the Firefox icon in the disk image!