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. MB wrote on

    What is the solution for people running older versions like v55 and below?

  2. John wrote on

    And for the possibility to install add-ons, is there a fix for that already ?

  3. Alex wrote on

    Thank you Mozilla, very cool!

  4. David S wrote on

    Verified that fix has been applied in about:studies. Add-ons are STILL DISABLED. When is this going to be fixed ?

    1. Kev Needham wrote on

      What version of Firefox are you using?

      1. NoName wrote on

        He’s probably like most of us, using FireFox Quantum 66.0.3 which is up to date and still isn’t working after your enable “studies” fix although the study does show as active.

      2. Roadrunner wrote on

        I was on 59 and studies were applied but fix was not working.
        Updated today to 66 and the addons started immediately

      3. Tom Sydow wrote on

        My add-ons also still don’t work, and when I look at my active studies, the ones you mention are not showing up. Please help

      4. anon wrote on

        The same for me. Version 66.0.3

      5. Berri wrote on

        I have the same problem as David, the study is installed but my addons are still disabled. FF 66.0.3 x64 on Win10 x64.

        1. Berri wrote on

          Forgot to mention that the installed study is “hotfix-reset-xpi-verification-timestamp-1548973”. The other one is not installed (yet?).

      6. Sad wrote on

        Verified but not working, i’m on Mac os High Sierra and that’s won’t work after the fix with the hotfix.

      7. kashif wrote on

        What about those of us on ESR 52.9.0 ? Will the fix work for us too?

      8. Balaji T K wrote on

        Am having same issue, running 66.0.3 (64-bit)

      9. ribogushter wrote on

        I am on 66.0.3 64-bit, same with me.

        1. ribogushter wrote on

          Actually, I’m wrong. The study I have is hotfix-reset-xpi-verification-timestamp-1548973. Got tricked by the same number, the description is different though 😉

        2. burice wrote on

          yap, exactly the same as me!!!!
          using 66.0.3 and all addons are disabled! repeating: ALL addons are disabled!

      10. John wrote on

        how will the fix be enabled for mobile browsers? Ublock Origins and HTTPS Everywhere stopped working this morning. On 66.0.2 on Android 8.0 LG G6.

      11. :( wrote on

        v 56.0.2

    2. David wrote on

      Mine didn’t come back until I changed app.normandy.run_interval_seconds to 1 in about:config and restarted FF. Once they came back, I set it back to 21600.

    3. firefox user wrote on

      Same problem here. Fix has been applied in about:studies, but addons are still disabled. I use version 66.0.3 (64-Bit)

      1. Tartar wrote on

        Same here. Desktop version 66.0.3 64 bit. Fix active but no one extention back & still disabled. Tried to remove and put one of addons again, but I cannot since the mistake appears “Loading was not successful. Please, check your connection.”

    4. Blake T wrote on

      Still waiting for this fix!!! really annoying to be inundated with google ads everytime I try to enter a site!! The more you guys try to be like Microsoft IE the worse your product becomes!!! used to be the best browser available, now its has become mediocre at best

    5. Kwyjor wrote on

      My addons only started working again after I disabled and re-enabled each of them in Tools -> Addons. (66.0.3 64-bit, to be clear.)

    6. ribogushter wrote on

      Same here.

    7. Hazel wrote on

      “Verified that fix has been applied in about:studies. Add-ons are STILL DISABLED.” I have the same problem and am running Firefox 66.0.3 (64-bit)

  5. Marcos wrote on

    Thanks guys!

  6. Mark Lewis wrote on


  7. leo_thekid wrote on

    Still not helping. Sync Now still not working.

    1. Kev Needham wrote on

      What version of Firefox are you using? Additionally, there are two studies that address this issue, and the study that needs to be active if you have disabled extensions is the “hotfix-update-xpi-signing-intermediate-bug-1548973”.

      1. Desipio wrote on

        Using the 66.0.3 version and it still doesn’t work for me. I have the fix installed.

      2. Tim wrote on

        So where is “hotfix-update-xpi-signing-intermediate-bug-1548973”? I have “studies” enabled, but this “study” is nowhere to be found.

      3. jeski wrote on

        I’m runnning 66.0.3 on win 10, and no change.

        these studies are active:

        1. Roberto Venturi wrote on

          I have hotfix-reset-xpi-verification-timestamp-1548973 active
          the other hotfix-update-xpi-signing-intermediate-bug-1548973 is not present

          Firefox x64 66.0.3 on windows7

        2. jeski wrote on

          I’ve been able to add my extensions back in, but did so manually. I’m wondering will an update be done that restores extensions automagically?

      4. Michael wrote on

        How is that one enabled? I have to other that shows active but not the hotfix update.

      5. Scott Seguin wrote on

        I’m using v66.0.3 and that particular hotfix is showing complete.

        prefflip-push-performance-1491171 is showing active

        But none of my extensions work still.
        Will have to use a different browser until this is fixed…. sigh 🙁

    2. David wrote on

      Even though I already had “studies” enabled and saw the hotfixes, mine didn’t come back until I changed app.normandy.run_interval_seconds to 1 in about:config and restarted FF. Once they came back, I set it back to 21600. (found on Twitter but the source was on Reddit)

      1. Shawn wrote on

        This worked perfectly – thanks so much. Your fix should be pinned to the top!

  8. M wrote on

    I see this and it is active in my firefox version 56.0 64 bit but my extensions are still disabled and i refuse to update because of the new way extensions must ask API’s to please do some things, instead of the old way which just replaces or overrides code to add remove or modify function.

    cant use tree style tab, cant use load tabs progressively or reload tabs progressively with the newest versions of firefox.
    my sessions start with 474 tabs and your latest version cant handle that.

  9. L Groeneveld wrote on

    thank you for addressing the issue on a saturday. seeing as i was in the middle of fiddling with options i do not know anything about, i panicked and thought to have messed things up myself. could have ruined my weekend, so thank you once more…

  10. Alexander Martin wrote on

    Using Studies to fix this is an interesting solution. Unfortunately, I am for some reason unable to enable Studies (I suspect it is due to my Linux distribution’s packaging). I’ve disabled addon signing on my installation for now until the update comes out.

  11. Kirsten wrote on

    The hotfix is in the completed section under Studies, but majority of add-ons and themes remain disabled.

    1. Kirsten wrote on

      It should be noted that I am using 66.0.3 (64-bit). I was on a slightly older version, when the add-ons got disabled, then I updated, thinking it might fix the issue (before I saw this article).

  12. Graham Perrin wrote on


    To clarify:

    > … up to six hours for the Study to be applied …

    – six hours after activation, yes?

    1. Graham Perrin wrote on

      … it seems that I was bugged, for a while, by

  13. Android? wrote on

    What about Android?

  14. Alphos2000 wrote on

    If I use an old version of firefox that I do not want to update… I won’t be able to use it anymore with my addons because of that? I’m forced to update my browser?

  15. Chris James wrote on

    I have the study applied on mine and still no fix…

  16. mikey wrote on

    What about Firefox on Android? There is no such setting there. Almost all of my addons are disabled there.

    Using the latest version available on the play store.

  17. Vincent wrote on

    Don’t work for me…
    Firefox quantum 66.0.3 (64bit) spanish version.

  18. elise wrote on

    thanks for the updates and info. it feels better to know the issue is acknowledged and being wrassled.

  19. kalvn wrote on

    I confirm, thanks to that tip my add-ons are back, thanks!

    Good luck with fixing the issue completely.

  20. Matthias wrote on

    Sorry,i am open firefox and after 20 minutes i have the same error.It dosen’t work for me.

  21. josh wrote on

    hey Kev, could you pls explain what are these Active/Complete statuses exactly?
    do i need to keep studies enabled until the one related certificates changes to Complete?

  22. Koga wrote on

    Works properly after enabling the studies option. Is it possible to disable it now ?

  23. Susan wrote on

    Thank goodness I found this blog post after all my add-ons and theme suddenly disappeared last nite. But the article wasn’t easy to find, and I think it would have been helpful to have put out an up to date announcement on the browser. Thanks tho for finding a way to fix. Love my Firefox, and all I kept finding was articles saying some add-ons had been disabled a year or more ago with Release 57, which made no sense since my addons were working on Beta 66.

  24. luion wrote on

    Firefox Nightly is currently not run with xml error. Nevertheless, does it become an automatic updating?

  25. Karel P. wrote on

    Fix not working here, few hours after enabling studies.
    Restarted browser a few times, but fix not showing in “Active studies”

    Apparently it’s not working for everyone.

  26. 11 wrote on

    version 52

    not working

  27. Mark wrote on

    Does this only appear if you have received the fix? Because my about:studies Is just a blank white page.

    FFQ Version: 66.0.3

  28. homie wrote on

    Study-Fix works fine for me.

  29. Toby wrote on

    “It may take up to six hours for the Study to be applied to Firefox.”

    Is there any way for us to speed this up from our end? Can we manually force a refresh of the studies? This study is not showing up for me!

    “We’ll continue to provide updates on continued efforts on this post, and will share a more substantial update in the coming days.”

    Are you saying it will take DAYS to fix this by way of a normal Firefox update?! Am I understanding that correctly?!

    If I have to wait DAYS for a proper update, then I will have no choice but to abandon Firefox permanently.

    This incident has forced me to try Chrome again, and you know what? I’m actually liking Chrome a lot more than I liked Firefox! At least I can use extensions with Chrome.

  30. Nancy wrote on

    I have Windows Vista and can’t afford to get a new computer right now. Because I have Vista, the last version of Firefox I could get updated to is 52.9. Will this fix apply to my computer as well? My Avast Internet Security add-on has been disabled by Firefox. Avast add-on for this same software last year (on 06/02/18) when I renewed it worked fine with no problems and I was on version 52.9 then (that’s when it came out). I am hoping this fix will work for me as well. Since I don’t have a newer version of Firefox on my computer, I don’t have the “studies” selection option.

  31. Gerald W wrote on

    I am using Firefox Quantum 66.0.3 (64 bit)with studies turned on and the fix has not come thru or worked yet.

  32. george wrote on

    In your 2nd paragraph you state that No added steps need to be done.
    Then you say that you are using studies to Implement!!!!!!!!!!!!!

    Why don’t you have ALL users check to make sure that they haven’t UNCHECKED THE BOX NEXT TO STUDIES?

    If you assume that everyone is allowing info to be sent back to you guys, you might have some angry users….

  33. Romain wrote on

    Hi! No active study is listed on about:studies on Firefox version 66.0.3 (64bits), thus the problems remain and without uBlock, the web is very ugly… Is this normal?

  34. Daweb wrote on

    Sorry is not working in 66.0.3 no study appears in the activ list

  35. Evgenii wrote on

    hot fix is in active studies, but addons not working. FF 66.0.3 64-bit

    1. Evgenii wrote on

      ok, all working fine now

  36. george wrote on

    I just UNCHECKED STUDIES and my addons are back, thank you

  37. Thomas wrote on

    Will the permanent fix require the browser to be updated to version 66? This isn’t an option for me for my Firefox installation on my work laptop, central IT has it locked on version 60 for some bizarre reason.

  38. Sebastian Diaz Pena wrote on

    I reinstalled firefox to see if doing so fixed the problem but it didn’t. And I also lost my add-ons because of that. Now that I see that the patch is up I try to download the add-ons again from the store ( and it always says that there is a error in the download and I can’t install any add-on again.

    1. Sebastian Diaz Pena wrote on

      Nevermind, I guess it got fixed or something I can install the add-ons again

  39. average_joe wrote on

    After enabling studies I can re-install the addons, but they do not work at all. Addon icons in the menu toolbar show up as empty space, addon settings cannot be altered, addons do not appear do anything even if they show up as enabled. Version 66.0.3 (64-bit) Win 10.

  40. Tom Swiss wrote on

    Not only have you broken all my extensions, Twitter and Facebook now give a HTTPS error (see below.)

    And to fix it I have to give you access to mess with my browser more? Brilliant.

    Great example of why updates should be pulled rather than pushed, guys.


    Your connection is not secure

    The website tried to negotiate an inadequate level of security. uses security technology that is outdated and vulnerable to attack. An attacker could easily reveal information which you thought to be safe. The website administrator will need to fix the server first before you can visit the site.


  41. chris wrote on


    ALL my CONTAINER data are gone.

    I manage 4 different identity for my business. now they are GONE.

    I cannot believe I support this program since 2001, donate monthly, and you guys so callously pull this on users.

  42. Grant wrote on

    What about for Firefox mobile? I’m not able to access about:studies or enable it unfortunately 🙁

  43. Big Sur Scott wrote on

    Why don’t you also offer a link to download and apply the fix asap for those of us who have been unable to work because of this issue?? I have that feature and all others that send info turned off. So to be able to work again, I have to compromise my privacy and have Mozilla obtain data from me. That is a really rap solution to a problem that should have never occurred. Yeah, I know how much I paid for the browser but I have donated over the years and believed in Mozilla. I still have Netscape 1.1 in a retail box, that is how long I have been devoted to this browser.

  44. VI wrote on

    Just had this problem 30 min ago

    Update firefox to the last version

    Add-on still disabled

    No studies apply

  45. Julie wrote on

    Firefox version 66 browser add-ons not working as of today (right now). No option under settings like you suggested above to enable studies. Will Android apps be updated soon?

  46. heli kurkikka wrote on

    i cant download adblock for firefox

  47. Andre wrote on

    What about the Android version? I’m using the latest beta.

  48. Tony Q wrote on

    Hi Kev, have you pushed the Studies based fix to Firefox on Linux? I have Studies enabled on Firefox 66.0.3 for Linux and haven’t gotten the fix yet. I see other Studies active though.

  49. hmm wrote on

    So, the ESR version has to wait for the “real” solution?

  50. Mouryan wrote on

    Fix worked, thankyou

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