Silent installation
Firefox has several methods for silent installation. The -ms switch and /S switch are both options although in Firefox 3.6 versions, the /S switch is currently broken (bug).
Mozilla recommends using the /INI switch for silent installation. Details can be found here: https://wiki.mozilla.org/Installer:Command_Line_Arguments
Import Wizard
The import wizard can be disabled by adding an override.ini file to "%PROGRAMFILES%\Mozilla Firefox\".
Add the following to the override.ini file:
[XRE]
EnableProfileMigrator=false
Application Updates
Many of Firefox's settings are controled through .js files within %PROGRAMFILES%\Mozilla Firefox\defaults\prefs\. The lines that control automatic updates are as follows:
pref("app.update.enabled", true);
pref("app.update.auto", true);
Simply change the true to false and application updates will be disabled.
Setting Firefox as the default browser
While the default browser can be set through the registry but Mozilla provides a much cleaner way to do so.
With Firefox closed, run the command:
firefox.exe -silent -setDefaultBrowser