Add-ons disabled or failing to install in Firefox

Incident summary

Updates – Last updated 14:35 PST May 14, 2019. We expect this to be our final update.

  • If you are running Firefox versions 61 – 65 and 1) did not receive the deployed fix and 2) do not want to update to the current version (which includes the permanent fix): Install this extension to resolve the expired security certificate issue and re-enable extensions and themes.
  • If you are running Firefox versions 57 – 60: Install this extension to resolve the expired security certificate issue and re-enable extensions and themes.
  • If you are running Firefox versions 47 – 56: install this extension to resolve the expired security certificate issue and re-enable extensions and themes.
  • A less technical blog post about the outage is also available. If you enabled telemetry to get the initial fix, we’re deleting all data collected since May 4. (May 9, 17:04 EDT)
  • Mozilla CTO Eric Rescorla posted a blog on the technical details of what went wrong last weekend. (May 9, 16:20 EDT)
  • We’ve released Firefox 66.0.5 for Desktop and Android, and Firefox ESR 60.6.3, which include the permanent fix for re-enabling add-ons that were disabled starting on May 3rd. The initial, temporary fix that was deployed May 4th through the Studies system is replaced by these updates, and we recommend updating as soon as possible. Users who enabled Studies to receive the temporary fix, and have updated to the permanent fix, can now disable Studies if they desire.For users who cannot update to the latest version of Firefox or Firefox ESR, we plan to distribute an update that automatically applies the fix to versions 52 through 60. This fix will also be available as a user-installable extension. For anyone still experiencing issues in versions 61 through 65, we plan to distribute a fix through a user-installable extension. These extensions will not require users to enable Studies, and we’ll provide an update when they are available. (May 8, 19:28 EDT)
  • Firefox 66.0.5 has been released, and we recommend that people update to that version if they continue to experience problems with extensions being disabled. You’ll get an update notification within 24 hours, or you can initiate an update manually. An update to ESR 60.6.3 is also available as of 16:00 UTC May 8th. We’re continuing to work on a fix for older versions of Firefox, and will update this post and on social media as we have more information. (May 8, 11:51 EDT)
  • A Firefox release has been pushed — version 66.0.4 on Desktop and Android, and version 60.6.2 for ESR. This release repairs the certificate chain to re-enable web extensions, themes, search engines, and language packs that had been disabled (Bug 1549061). There are remaining issues that we are actively working to resolve, but we wanted to get this fix out before Monday to lessen the impact of disabled add-ons before the start of the week. More information about the remaining issues can be found by clicking on the links to the release notes above. (May 5, 16:25 EDT)
  • Some users are reporting that they do not have the “hotfix-update-xpi-signing-intermediate-bug-1548973” study active in “about:studies”. Rather than using work-arounds, which can lead to issues later on, we strongly recommend that you continue to wait. If it’s possible for you to receive the hotfix, you should get it by 6am EDT, 24 hours after it was first released. For everyone else, we are working to ship a more permanent solution. (May 5, 00:54 EDT)
  • There are a number of work-arounds being discussed in the community. These are not recommended as they may conflict with fixes we are deploying. We’ll let you know when further updates are available that we recommend, and appreciate your patience. (May 4, 15:01 EDT)
  • Temporarily disabled commenting on this post given volume and duplication. They’ll be re-enabled as more updates become available. (May 4, 13:02 EDT)
  • Updated the post to clarify that deleting extensions can result in data loss, and should not be used to attempt a fix. (May 4, 12:58 EDT)
  • Clarified that the study may appear in either the Active studies or Completed studies of “about:studies” (May 4, 12:10 EDT)
  • We’re aware that some users are reporting that their extensions remain disabled with both studies active. We’re tracking this issue on Bugzilla in bug 1549078. (May 4, 12:03 EDT)
  • Clarified that the Studies fix applies only to Desktop users of Firefox distributed by Mozilla. Firefox ESR, Firefox for Android, and some versions of Firefox included with Linux distributions will require separate updates. (May 4, 12:03 EDT)

Late on Friday May 3rd, we became aware of an issue with Firefox that prevented existing and new add-ons from running or being installed. We are very sorry for the inconvenience caused to people who use Firefox.

Our team  identified and rolled-out a temporary fix for all Firefox Desktop users on Release, Beta and Nightly. The fix will be automatically applied in the background within 24 hours. No active steps need to be taken to make add-ons work again. In particular, please do not delete and/or re-install any add-ons as an attempt to fix the issue. Deleting an add-on removes any data associated with it, where disabling and re-enabling does not.

Please note: The fix does not apply to Firefox ESR or Firefox for Android. We’re working on releasing a fix for both, and will provide updates here and on social media.

To provide this fix on short notice, we are using the Studies system. This system is enabled by default, and no action is needed unless Studies have been disabled. Firefox users can check if they have Studies enabled by going to:

  • Firefox Options/Preferences -> Privacy & Security -> Allow Firefox to install and run studies (scroll down to find the setting)

  • Studies can be disabled again after the add-ons have been re-enabled

It may take up to six hours for the Study to be applied to Firefox. To check if the fix has been applied, you can enter “about:studies” in the location bar. If the fix is in the active, you’ll see “hotfix-update-xpi-signing-intermediate-bug-1548973” in either the Active studies or Completed studies as follows:

You may also see “hotfix-reset-xpi-verification-timestamp-1548973” listed, which is part of the fix and may be in the Active studies or Completed studies section(s).

We are working on a general fix that doesn’t use the Studies system and will keep this blog post updated accordingly. We will share a more substantial update in the coming days.

Additional sources of information:

421 comments on “Add-ons disabled or failing to install in Firefox”

  1. Beba wrote on

    I was out, but just came back and the add-ons are back on!
    Both the hotfix-reset-xpi-verification-timestamp-1548973•Active and the
    are showing.
    I didn’t have to do anything, except re-download a couple of extensions that I had removed.
    Thank you Mozilla

  2. Moonthink wrote on

    I click the checkbox to “Allow Firefox to install and run studies”

    When I close the options tab, then click on options again, that box is no longer checked.

    I’ve had ff open for 5+ hours
    about:studies isn’t showing any studies active or completed

  3. Jerry Jonnson wrote on

    Wow… What a pile of whiny neurotic people out there… I guess it just shows that they really don’t have any life at all…

    1. Joey wrote on

      Complaining about a system that broke unexpectedly across the board isn’t whining. Read through some of the problems we’re having and maybe you’ll get it

  4. Samuel Vuorela wrote on

    Why not just post a link to the fix that can be installed WITHOUT enabling Studies? This sounds like a clever plan to get more people to share their data via Studies…

    The fix in question can be installed by clicking this link [1]. It’s signed by Mozilla.

    Thanks to user gpm at Hacker News, who posted this tip [2].


    1. asdf-anynomyous wrote on

      @Samuel Vuorela
      Thank you very much for this info!
      Suddenly my firefox browser disabled ALL add-ons, and I realized it when a webpage that I frequently visit suddenly displaying all kinds of adds. This really sucks. And, I tried sending studies and whatever it is but to no avail.
      Time to switch to Chrome or Opera

    2. Vincent Nerviano wrote on

      THANKS!! Instant fix. Ignored warning …..

    3. Aarhj wrote on

      So how do I get Firefox to install it, though? It tells me “The Add-on could not be downloaded because of a connection failure”, but my connection is obviously fine …

    4. FFuser wrote on

      Any need/way to uninstall it when the problem has been fixed properly?

  5. Don Barry wrote on

    I bitterly complained when centralized signing of addons was pushed by Mozilla, and now it has come back to bite them. In this case, their own hypocrisy was to blame. While crowing about software freedom and freedom of choice, they placed themselves as central arbiters in the add-on ecosystem, even to the point where local installations of addons required signatures without hacks to the Firefox config. Debian at least disabled signature requirements for local system directory installations, but it’s clear that Mozilla wanted to retain a monopoly on future “app stores” even as theirs makes not the slightest effort to show the licenses of individual addons and prioritize those which are free/libre.

    And each release brings with it a flood of new privacy-intrusive options and telemetry, requiring more and more byzantine methods to block. And two years ago, pushing out a browser which telemetered whether telemetry was turned off — even *when* it was turned off, requiring an undocumented variable to block, really showed the contempt Mozilla administration had for privacy-conscious users.

    The problem is, it’s still the least-bad of the browsers, though this could change rapidly. At least it is possible, though difficult, to maintain a privacy-conscious installation without source patches and the lengthy recompilations.

  6. Jim wrote on

    LastPass not working after receiving studies:
    Using 66.0.3 on OS X; Enabled studies – nothing happened until I changed app.normandy.run_interval_seconds to 15 in about:config and after restart received two hot fixes and a preference fix.

    Re-installed LastPass and uBlock Origin – both appear in Extensions as Enabled. Clicking on LastPass preferences results in endlessly spinning red circle. No LastPass icon in menu; no IDs/passwords filled; no access to LastPass preferences; no nothing. Do I have lots of work-arounds to be able to use Firefox and fill in passwords? Yes, but I’m not happy about manually doing what used to be automated. If not functioning in 24 hours, Firefox bookmarks get moved to another browser and I’ll get on with life (grateful that my time as a sys-admin including managing certificates is long past).

  7. Beki wrote on

    I’m on Win 10 firefox versoin 66.0.3 64 bit and I tried to load the studies page and it comes back blank. All of my add ons are still gone, so I am sure that I’ve not gotten the fix, but I would expect to see something on the studies page?

  8. dcm1028hk wrote on

    I was on 66.0.4 and studies were NOT applied
    Rest of past not working add-ons WORKING

  9. Peter Thompson wrote on

    What about those of us who are using a much older version because developers have not recoded their plugins for the newer releases of Firefox, and for which plugins there are no suitable replacements? I’m using 55.0.3. What steps will need to be taken to get those plugins to work again?

  10. Blah wrote on

    I’m finding this VERY annoying! Does anyone know when it will be fixed?

    1. ESR wrote on

      it is SUPER annoying. why don’t they just roll back?

      this sucks.

    2. ESR wrote on


  11. Helge wrote on

    Thank you!
    I was afraid I had to find another browser.
    But after this fix I’m still sticking with Firefox.


  12. PN wrote on

    My problem actually started about an hour ago. Up until then, anything worked, then suddenly all my addons stopped working. It was about the time Firefox announced the fix. But when I activated the studies, it shows there are no studies for me. WTF? What am I supposed to do to get that study and get my addons working again? It’s just unreal.

  13. dcm1028hk wrote on

    *** REVISED**

    I was on 66.0.4 and studies were APPLIED

    Rest of past not working add-ons WORKING

    1. ESR wrote on

      Download failed. Please check your connection.
      Preview of Google Shortcuts – All Google Services at a glance

  14. angryzilla wrote on

    ok they are back but all settings have been reset, any fix for that ?

    1. Meredith wrote on

      Same here–lost all of my meticulously curated settings for multi-account containers. Glad to see the quick turnaround on the fix (so appreciate the devs who worked overnight), but super sad to have to start from scratch on this!

  15. kostas_gr wrote on

    firefox 56.0.2 used, no “enable studies” option
    all add-ons stoped working and no new can be installed
    addon blocker or another like this needed
    update firefox to latest version is not an option because of non supported addons
    so what to expect? is there going to be a solution also for older firefox versions?

  16. George S wrote on

    I enabled the studies, but I still have not received the patches. I enabled add-ons manually. My Firefox version is 62.0.3 (32-bit) and it is locked.

    1. ESR wrote on

      same here

      THIS SUCKS!!

  17. Blink wrote on

    Thanks to the Firefox team for staying up late fixing this. Their work has all been logged publically at and clearly they were taken by surprise but worked hard to fix it overnight.

    Computers are complicated and tricky to get right. Something slipped through and they are fixing it. They even acknowledged this in a self-deprecating way with a cute name: “armagadd-on”.

    I have the fix now via Studies, but I never saw the symptoms. Anyone else *not* have a the problem? I did try installing from, and that was failing, but I didn’t have the problem of losing addons or their settings. My only addons are uMatrix and uBlock Origin, and they both kept working all night. I checked at 5pm PDT, 11PM PDT and 8am PDT. Firefox 66.0.3 (64 bits) OS X.

  18. Stefan wrote on

    doesnt work on my system. Maybe a reason is because i have installed the “enterprise policy generator” and deactivated all updates there (because I hate updates…). But I cant change the settings there now, because the enterprise-policy-generator-extention is disabled too. And I cant install any new extention too, what should I do?

    I’m very disappointed from firefox and think about to use an other brower

  19. Paolo wrote on

    No fix for Firefox on Android?

  20. Mr_Cadcam wrote on

    I wish I would have read this sooner …. I removed my “Legacy” themes and addons as Firefox displayed “Some Addons have not been verified”, or something very similar. Oh well, hopefully I can get them all back as they were.

  21. Mose wrote on

    There is a reason I have studies turned off. Now, Mozilla is forcing everyone to turn studies on. As of today, I trust Mozilla about as much as I trust Microsoft and Google.

    1. Nick Animus wrote on

      I second that.

  22. Steven wrote on

    Huge fan of Firefox, but this one really annoyed me.
    Despite the fact that I have to active data collection (which was my original reason to stop using Opera and Chrome) to temporary fix this mess, the multi-account container addon seem to be completely messed up. My custom containers are gone together with all the site settings. This will take a bit to reconfigure everything.

    We can just hope you’ll learn out of this so this doesn’t happen anymore.

  23. StopRemovingOptions wrote on

    So will you put back the option in about:config to disable mandatory signing now ?
    You really should listen to your users more.
    Automatic reviews on AMO with automatic signing make this whole thing useless against dangerous addons. Mandatory human review on AMO !

    Hopefully this will be eye opening for you guys, stop removing customization and useful option for power users !

  24. Ralph wrote on

    For users, who run an old Firefox like version 52 ESR or on their Android device, a temporary fix could be, when you go to “about:config”, search for “xpinstall.signatures.required” and set it to False. But don’t forget to set it back to True, when your Firefox gets a real working fix.

  25. DenIrenicus wrote on

    I have turned off “Firefox Data Collection and Use” completely and will wait for the new version of FF with the fix inside.

  26. VI wrote on

    Cant we download the hotfix or studies on our own ?

    It will be faster

  27. Jack wrote on

    Studies system were enabled, fixes are received, but they didnt help at all, even after restart. Win7, FF 66.0.3.

  28. steyin wrote on

    The fix in Samuel’s post above restored addons but gmail still won’t load.

  29. Metalsmith wrote on

    Moonthink, I too have the same issue. I can enable studies by checkmark. close the options tab and re open it and it’s unchecked again. Going to the learn more or about:studies page displays this, “This is a list of studies that you have participated in. No new studies will run.”

    I’m running Firefox 64.0.2

    Let me know if you find any work around.

  30. Sir Jon wrote on

    The studies hot fix has been applied here and still all the extensions are disabled and listed under legacy.
    So when is it going to be fixed properly?

  31. Caroline wrote on

    Applied the quick fix and my ad-ons are working again.

  32. Andy wrote on

    Last night not knowing the problem I completely removed add-ons. Will this patch/study allow me to add them back, or does it only fix what was disabled but not removed?

  33. B Doyle wrote on

    It’s 11:44am Central Time USA. I have “hotfix-reset-xpi-verification-timestamp-1548973” as “ACTIVE”, but I still cannot download addons and none of them work, like NoScript or ADBlocker Plus. I get a popup stating (when on the site that: “Firefox prevented this site from asking you to install software on your computer”. I click allow, then I get a popup stating “The add-on could not be downloaded because of a connection failure.”, and I get this for NoScript and all the others.

    I really want to be able to safely do things on the internet. I hope it is fixed soon.

  34. Roger wrote on

    There is no ‘Firefox Preferences -> Privacy & Security -> Allow Firefox to install and run studies.’ within Options???????

  35. Sean wrote on

    THIS IS NOT FIXED. Firefox does not update to correct this.

    FIX IT, please.

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