Firefox Preferences Monitor gets pref cleaning capabilities

Martin Brinkmann
Nov 13, 2013
Updated • Apr 26, 2015
Firefox, Firefox add-ons

The Firefox web browser would not be where it stands today without its add-ons and the community behind it. They add, change or remove functionality from the stock browser giving users options to customize it in thousands of different ways.

Recently, that is in the last one year period, they have also been used to revert changes that Mozilla made to the Firefox web browser.

One issue that I addressed years ago in this regard is that add-on preferences do not get cleaned up when you uninstall the extension in Firefox.

What this means is that the file holding all those information grows over time, and that you will still see the preferences when you access the about:config page in Firefox.

While it is possible to go through the prefs.js file manually to remove all obsolete entries in it, it is usually not the best approach as it is quite easy to break the file which can result in numerous issues.

Preferences Monitor

Back in 2011 I reviewed Preferences Monitor and ECleaner for the first time. They were independent add-ons then that enabled you to monitor Firefox preferences and to remove obsolete entries from Firefox's configuration.

These two extensions have now been merged into one. While that is the case, they work independent of each other for the most part.


preferences monitor interface

The monitoring part of the extension watches Firefox's about:config for changes and notifies you so that you know what has been changed.

The extension uses the Browser Console for that, which unfortunately hides the output somewhat. There are notifications on top of that though for changes that are not whitelisted, so that you know what is going on even if you do not open the browser console at all.

Preferences Monitor can do more than just monitor what is going on though. You can configure it to ignore certain preferences and to revert changes automatically made to select matching preferences. You do need RegExp skills for that though.

Other options include saving the log to a text file, preventing notifications for select preferences, and a Preferences Guard which I think blocks changes from being made in first place. There is no explanation attached to the option though and I was not able to trigger it during tests.


clean preferences

You can launch eCleaner from the add-on page. It opens in a new tabbed window. The four tabs display the following information to you:

  1. Extensions lists all preferences created by extensions. Please note that this includes preferences from extensions that you have installed in Firefox at the time of running eCleaner, and past extensions.
  2. Profile displays folders and files stored in the profile folder.
  3. Downloads lists all downloads that have been made since the last clean-up.
  4. LocalStore highlights local pages and their data.

Note: You need to be very careful when you are using the tool, as it mixes old and existing preferences and information. Make sure you know that an entry is obsolete before you click on the remove selected button.

You can select one or multiple items here for cleanup. Just select them and hit the remove selected button afterwards to do so.

If you are looking for a specific preferences, use the filter at the bottom of the screen to find it faster.

The extension offers to restart Firefox after you have deleted entries.

Closing Words

Preferences Monitor is an advanced tool. While the monitoring part of it has its uses for all Firefox users, especially those who do not want extensions or programs to modify settings in the browser, its eCleaner part is only suitable for users who know what they can clean and what is better to be left alone.

The extension could use some updated control options, like a toolbar button of sorts that you can click on to improve its accessibility. While the developer suggests to create one of your own, it would be easier to ship it directly with the extension instead.

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Preferences Monitor
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  1. Ken Saunders said on November 15, 2013 at 1:06 am
  2. Ken Saunders said on November 15, 2013 at 1:00 am

    It’s silly that an add-on as sophisticated as this one doesn’t offer a less cumbersome way to launch it’s main interface. If it had more users, I’d create a better way myself.
    You can just bookmark chrome://prefmon-ecleaner/content/ecleaner.xul and perhaps use a keyword to open it in a new tab, but it’s a preference window with set dimensions so the browser gets resized to those dimensions (then you have to resize the browser). It’s not a huge deal and it’s faster and easier to access than the default method of 3 to 4 clicks and going through menus, etc.

    With that being said, it is a good add-on.

  3. Mystique said on November 14, 2013 at 8:51 am

    another option is ffp-cleaner which can be found at

    Preference cleaner is no longer available at the official Firefox extension site but can still be downloaded at softpedia: [the link is no longer available]

  4. WandersFar said on November 13, 2013 at 10:16 pm

    Are stuck preferences the reason why uninstalled addons still show up in CCleaner’s scans of my Firefox profiles?

    I got rid of Stylish some time ago but the extension still shows up in CCleaner under Tools » Startup » Firefox. Any tips how to remove it? I tried manually deleting the one reference to Stylish in my prefs.js but it still shows up in CCleaner, although not in about:addons.

  5. Karl J. Gephart said on November 13, 2013 at 6:55 pm

    eCleaner is good, I used to use it, but I like the Preferences Cleaner addon even better. I delete leftover entries in the “uninstall extensions” tab, and then check the “Lose Preferences” (3rd menu button), to make sure they are gone, or delete them there, if necessary.

  6. Ficho said on November 13, 2013 at 3:48 pm

    Is it still safe to use eCleaner 1.4 ?
    I see that developer name is changed.

    1. Martin Brinkmann said on November 13, 2013 at 4:14 pm

      Well he has integrated the extension in Preferences Monitor. I would switch as the other app won’t be updated anymore it appears.

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