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MacEnterprise: Managing FireFox

Volume Number: 24
Issue Number: 12
Column Tag: MacEnterprise

MacEnterprise: Managing FireFox

Configuring FireFox for your organization's environment

By Greg Neagle,


Although Safari is an excellent web browser, many organizations need to support Firefox as well for a variety of reasons. One very good reason is that it is a modern browser that runs natively on Windows, Linux, and OS X. If your organization supports multiple platforms, it makes sense to standardize on cross-platform applications like Firefox and Thunderbird when possible.

If you are supporting Firefox as a browser in your organization, you may need to pre-configure it for users in your environment. You may need to set up proxies, define your organization's home page as the default browser home page, and turn off application updates, among other things.

Unfortunately, Firefox does not respond to the Mac OS X administrator's standard bag of tricks for managing it. Workgroup Manager/MCX is of no use here, as the important settings are not stored in the org.mozilla.firefox.plist file in the user's preferences. By default, Firefox pays no attention to the system proxy settings. Even such time-honored tricks as copying in pre-defined preference files can be difficult with Firefox as it stores the user profiles at different paths, generated on the first run of Firefox.

A New Bag of Tricks

To manage Firefox in an enterprise environment, you'll need to learn a new bag of tricks. There are two things to learn:

How Firefox defines its preferences.

Where to define your preferences so Firefox will use them for all users on a given machine.

Firefox Preferences

Firefox is a descendant of the Mozilla browser, which was in turn descended from Netscape. Many of the mechanisms carry over from those browsers, and if you are looking for documentation on the Internet, you might want to broaden your search to those browsers as well.

Firefox uses JavaScript files to define its preferences. There are three JavaScript functions defined by Mozilla/Firefox you might use:

  • pref() - sets the current value of a preference. Useful for preferences you'd like to reset to defaults for each session, but to allow users to change during a session.
  • lockPref() - sets the value of a preference, and locks it so users can't change it. Useful to enforce certain policies.
  • defaultPref() - sets the default value of a preference. If the user has already set a value for this preference, this will have no effect.

What preferences can be set? You can get an idea of the vast array of available preferences by opening a Firefox window, and typing about:config into the URL field. If you are running Firefox 3, you might see a warning:

Ignore the sensationalism and click the "I'll be careful" button. You'll see a long list of available preferences:

Some of these correspond to preferences you can access from the Preferences window in Firefox, and others are hidden preferences. The important thing here is that you can get the preference name, its status, type and value, which you'll need in order to manage the preference.

In theory you can manage any of the preferences you find in about:config, but for this article we'll look at a subset. We'll explore how to manage proxy settings, the default browser check, and application updates. We'll also look at changing the default home page, but that actually uses a different technique, which we'll save for later.

Proxy Settings

To get started with managing the proxy settings, first configure them manually, using the Preferences window in Firefox:

In this example, I'm using an automatic proxy configuration URL, sometimes referred to as a "PAC file". Click OK, and once again, visit about:config. To narrow down what is displayed, type "proxy" in the Filter field:

The values we've set will have a status of "user set", and display in bold:

You can use a similar process to determine the correct names and values for most of the preferences you'd like to manage.

Here are the rest of the preferences we're going to manage for this article:

These control application and extension updates, updating the list of available search providers, and the check to see of Firefox is the default browser at launch. Since we are managing Firefox, we don't want users to be notified of newer versions of the application or extensions, and we don't want the user constantly prompted to set Firefox as the default browser.

Editing the Firebox Bundle

To actually get Firefox to use your desired preferences for all users of a given machine, you'll need to edit some files inside the bundle. You'll need to do the editing as either root (via the command line, perhaps using sudo), or as the owner of the files in the Firefox bundle; typically the admin user that installed Firefox.

Take care when editing. If you use a GUI editor, make sure you save any new or changed files as plain text and that no extra extensions are appended to the end of the filename.

You will start by editing the file /Applications/

Add the following to the end of this file:

 // MyOrganization additions
pref("general.config.obscure_value", 0);
pref("general.config.filename", "firefox_AA.cfg");

Feel free to change "MyOrganization" to the actual name of your organization. What we're doing here is telling Firefox to read the file named here for additional configuration info. The "general.config.obscure.value" tells Firefox the file will be in plain text; by default it expects the file to be obscured with ROT13 encoding, where 13 is added to the ASCII value of every character. The reasons for this are lost in the mists of antiquity.

Save the /Applications/ file. Now create a new file at /Applications/ with the following contents:

// This file sets some prefs for use at MyOrganization
// and locks down some other prefs.
// set proxy config
pref("network.proxy.autoconfig_url", "");
pref("network.proxy.type", 2);
// disable application updates
lockPref("app.update.enabled", false);
lockPref("app.update.autoUpdateEnabled", false);
lockPref("extensions.update.enabled", false);
lockPref("extensions.update.autoUpdate", false);
lockPref("", false);
// disable default browser check
pref("", false);

Again, make sure you save it as a plain text file with the name "firefox_AA.cfg" in the directory "/Applications/". Double-check your work via the command line:

> cd /Applications/
> ls -al firefox_AA.cfg 
-rw-rw-r—  1 admin  admin  636 Jul 23 13:22 firefox_AA.cfg
> cat firefox_AA.cfg

That last command (cat firefox_AA.cfg) should return the exact contents you entered when you created the file.

In this example, we used two different commands: pref(), and lockPref(). For the proxy, I wanted the user to be able to modify the proxy if needed, but have it return to our recommended settings on the next launch. For the application updates, I wanted to prevent the user from turning these back on. Your requirements may differ.

With everything saved and double-checked, try launching Firefox. You should find these settings exactly as you specified, and in the case of the update prefs, locked:

Note how the corresponding controls are grayed-out and unavailable.

Default Home Page

One important preference is a little harder to manage: the default home page. You might get a clue of why this is so by looking at the preferences in about:config:

You'll see that the browser.startup.homepage points to another file, instead of just being a normal URL. You can set it to a normal URL, and it usually works, but I've found it unreliable. So instead of setting a preference, we'll edit the contents of

Open /Applications/, delete its entire contents, and replace them with:


Of course you want to substitute your own URL for the home page.

Now quit and relaunch Firefox. Unless you've set a custom home page, you'll be taken to the home page you defined. Users have the ability to override this if they want. If you truly wanted to enforce a home page, adding

pref("browser.startup.homepage", "");
pref("browser.startup.homepage_reset", "");

to /Applications/ should get the behavior you want, but your users may dislike you.

Now that you've modified the bundle, you'll need to push out these changes to all your machines. I hope you have a software distribution mechanism in your organization!

More Info

Congratulations! You've added a few new tricks to your toolbox. For more information on Mozilla/Firefox preferences and configuration, check out these URLs:

Greg Neagle is a member of the steering committee of the Mac OS X Enterprise Project ( and is a senior systems engineer at a large animation studio. Greg has been working with the Mac since 1984, and with OS X since its release. He can be reached at


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