Beware! Firefox updates may reset preferences

Martin Brinkmann
Dec 5, 2016

Mozilla releases updates to Firefox Stable regularly. The organization did so on a six week schedule in the past, but has loosened that up a bit in recent time.

This schedule bumps the number in front of the dot by one. Smaller updates may increase the number after the dot to fix smaller issues or introduce changes to the browser.

Firefox Beta, Developer and Nightly versions are updated more frequently than the stable version.

Firefox updates should not have any impact on a user's custom configuration of the browser. There are a couple of exceptions to the rule. One is, if Mozilla decides to remove a preference from the browser, or rename it.

Beware! Firefox updates may reset preferences

firefox reset preferences

I was contacted by two Ghacks readers in the past two weeks about Firefox resetting preferences of the web browser during updates.

Jern informed me that Firefox reset the block lists setting of the browser's Tracking Protection feature from strict to basic when the browser was updated to version 50 from Firefox 49.0.2.

Basic protection is the recommended and default value of the setting. It does not block as many trackers as the strict blocking list.

I confirmed that the upgrade to Firefox 50 did indeed reset the preference.

Michel told me a week later that a recent Firefox update (to 50.0.1 or 50.0.2) did reset another preference. This time an URL string that Michel modified on Firefox's about:config page.

As you may know, you can modify hundreds of preferences on about:config. Some allow you to change URLs that Firefox uses. In this particular case, Michel modified the URL responsible for pulling add-on suggestions on the about:addons page of the browser.

And it was this URL that reset when Firefox updated to one of the newer versions.

The two users noticed the changes because they impacted how they use the browser. While those two are confirmed -- I confirmed the resetting using a local copy of Firefox -- there is no telling if other preferences were also reset in recent time during updates.

Closing Words

I can't come up with reasons why resetting those two preferences was justified.

As I said earlier, it may make sense to reset preferences for a variety of legitimate reasons. This should only happen however if it does not impact a user's customization provided that it is still valid.

Since both basic and strict protections are still available, and since it is possible to change the URL of the add-ons suggestions page, I'm puzzled why the preferences were reset.

Now You: Did you notice the resetting of Firefox preferences during updates?

Beware! Firefox updates may reset preferences
Article Name
Beware! Firefox updates may reset preferences
Mozilla Firefox may reset custom browser preferences when the web browser is updated to a newer version so that the preference is set to its default value.
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  1. Jeff said on January 30, 2021 at 12:30 am

    Four-plus years later (and presumably after thousands of complaints from users to Mozilla) an update still deletes all your own preferences and resets to defaults, many of which are very annoying (such as NOT opening pdf files with Adobe Reader) and others that eliminate basic functionality that a majority of users prefer.

  2. pHROZEN gHOST said on December 7, 2016 at 4:47 pm

    I keep ZIPped backup copies of my FF folders so I can go back if something unexpected happens

    Before an update, copy your prefs.js to prefs.before.js. After the update, compare the prefs.js to prefs.before.js.
    WinMege is a good tool for comparing files or even whole directories.

  3. Ted said on December 7, 2016 at 8:08 am

    I updated Firefox 64-bit in Windows 8.1 to version 50.0.2. It didn’t reset settings. Even if it had I would have set them back with Mozbackup.

  4. Pants said on December 7, 2016 at 7:00 am

    @hmm .. pocket is a “system” addon
    – first remove the icon from your toolbar
    – second change these settings in about:config (just the 1st one should be sufficient)
    user_pref(“extensions.pocket.enabled”, false);
    user_pref(“extensions.pocket.api”, “”);
    user_pref(“”, “”);
    user_pref(“extensions.pocket.oAuthConsumerKey”, “”);
    – third, remove the actual extension, which is located at /browser/features/ (I’m using portable versions, so for installed ones I am not sure where exactly this is under user/appdata or if it’s under program files

    Note: being a system addon, it will return EVERY update you install.

  5. hmm? said on December 6, 2016 at 4:25 pm

    Anyone else having problem turning Pocket off in about:performance in newest Fx? In 49 was everything fine, but in newest version I can disable/unistall every addon except Pocket (clicking disable/unistall does no effect).

    1. Ted said on December 7, 2016 at 8:10 am

      Hide it in the Customization panel.

      1. hmm? said on December 7, 2016 at 4:45 pm

        Hide it, don’t disable it which can be check at about:support

        @Pants Already done about:config part. In files, I find out there’s [email protected] in /usr/lib/firefox/browser/features/ but it’s not easy deletable in Linux. Anyone know if it can be done with some command in terminal?

        On Windows, Pocket could be disabled by CCleaner.

  6. max said on December 6, 2016 at 11:35 am

    What’s the bugzilla-ticket-number for this bug?

  7. bwsHomeU said on December 6, 2016 at 5:12 am

    Do these reset changes apply to FF ESR as well?

  8. Croatoan said on December 5, 2016 at 7:08 pm

    – Custom history reset to Remember history
    – Block list changed
    – Enabled crash reporter

    Thanks for heads up, Martin.

  9. Anonymous said on December 5, 2016 at 4:14 pm

    People using a good ad-blocker like uBlock Origin will never have this kind of anxiety.
    People trusting Mozilla in that way should revise their theory.

  10. SCBright said on December 5, 2016 at 2:41 pm

    Just use FEBE to backup and restore your preferences.

    1. Tom Hawack said on December 5, 2016 at 3:18 pm

      The FEBE add-on performs a backup of the user’s profile(s). Be it with FEBE or with a manual backup I would strongly advise *against* restoring a profile taken with a previous version of Firefox to a new version of the browser.

      There are settings and data which are version-specific, besides those tweeked by the user, which can lead to problems when overwritten with those from a previous version. The user’s user.js file (in his profile folder) is never modified by a new version but a new version may very well add, modify other data/settings of the user’s profile data so overwriting them may lead to problems.

      I’ve read/seen more than once users confronted to these problems because they inconsiderately overwrote their profile folder with a backup made at the time of a previous Firefox version : restore a profile version ONLY within the same Firefox version.

      1. Jojo said on December 9, 2016 at 9:31 am

        Thanks for the headsup Tom!
        I’ve used FF years ago, and had lots of add-ons and customizations etc…
        Had it all FEBE backed up, and after years of chrome only, I’ve recently came back to FF [all due to using an old system with old ram and tendency to have multiple windows with multi-multiple tabs opened…] ….
        So, I guess throwing FEBE on my current FF isn’t a good option, But it sure is good to have my old add-ons list backed up…
        GL&HF :)

  11. anon said on December 5, 2016 at 12:58 pm

    It could be a bug. Maybe something changed internally that required resetting the preference in order to avoid issues? The software is open-source, after all!

    1. Martin Brinkmann said on December 5, 2016 at 1:13 pm

      Sure that is without doubt a possibility. I’m not saying Mozilla did so deliberately as there is no proof of that.

  12. Tom Hawack said on December 5, 2016 at 12:42 pm

    I haven’t noticed the resetting of Firefox preferences during updates, maybe because I systematically add to my FF’s profile user.js file whatever modification of the about:config settings. What is described in this article is what happens to a setting in about:config which has been modified by the user right on that page only, and that I cannot confirm by my experience even if I acknowledge this unorthodox browser behavior.

    This confirms that the best way to have a setting fixed and remained fixed is to include it in the user.js file. On the other hand settings which disappear in a new FF version will inevitably be re-written should the user have included them in that user.js file. This won’t harm as such but besides insignificant bloat may mislead the user because he believes in a given setting in the user.js file when in fact the setting would have become obsolete.

    If the user is committed to his tweaks & settings then it’ll require perspicacity and work especially with updated versions of the browser. Nothing is static and remaining zen in an increasingly dynamic world is a challenge.

  13. neil said on December 5, 2016 at 12:36 pm

    Thanks for this.

    The 2nd change in about:config you mention – What exactly was changed? What is impact of this ‘reset’?


    1. Martin Brinkmann said on December 5, 2016 at 12:52 pm

      The old URL was reset, so that add-on suggestions were once again displayed.

      1. neil said on December 6, 2016 at 5:45 pm

        not sure where would see this list so not sure missing something obvious or not

  14. Yuliya said on December 5, 2016 at 12:12 pm

    extensions.webservice.discoverURL is the add-on suggestion page? I have it set to none (empty) and it did not reset after v50 updates (all of them, currently 50.0.2). I remember to have blocked everything related to disconnect_me in about:config, which also seems to be as I left it.
    That being said, v50 seems half-arsed, visual glitches for the most part, but they were not present in v49.

  15. MikeFromMarkham said on December 5, 2016 at 11:41 am

    Martin, thanks for the heads up about the reset of the block lists. I also experienced a change in settings from strict to basic, which I changed back immediately.

    No idea why Mozilla would think it’s a good idea to change user preferences without warning or confirmation.

    Firefox is NOT windows 10.

  16. David said on December 5, 2016 at 9:51 am

    Remember you can use Windows’ “Previous Versions” feature to restore an older version of your profile folder or prefs.js

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