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. Daniel S. wrote on

    I’m using Firefox version 56.xx for reasons. Is there also a fix for this version available?

    1. nobody wrote on

      Doesn’t look so… I’m also using FF 56 (cause I need some of the older extensions), and nothing seems to work. I’ve tried to change the values in about:config (which seem like the part od hotfix for newer versions), changing date, enabling debuging mode – still nothing. I hope, that i hadn’t lost my data within addons…

      Mozilla – you are a joke. So simple error, the internet is boilng about that issue, hours later… nothing.

  2. Billy wrote on

    My firefox still not fix. version Firefox Quantum 66.0.3 (64 bit).No update nothing change.

  3. Moleculor wrote on

    You say this may take up to six hours to happen automatically.

    How do I make it happen now?

  4. Cjay wrote on

    My add on”s are still unsupported. Anyone else? 10:45 a.m.

  5. Kate C wrote on

    Trying to ‘Find a Replacement’ for many extensions and get the response that “Download failed. Please check your connection.’ – but my connection is fine. i managed to retrieve 1 of the extensions you deem unacceptable. now 9 AM CST. any idea when i can go online feeling secure? just asking.

  6. John Massaro wrote on

    10:44 AM EDST, Add-ons are still disabled

  7. Paula wrote on

    I was attempting to fix this issue on my dad’s computer last night before I knew the issue was more widespread. I ended up just removing the add-on (Adblock Plus) entirely. Do I need to do anything different to put the add-on back on his Firefox, or will the fix allow me to install it back on Firefox? Thank you!

  8. TomatoSoup wrote on

    I have enabled studies. The study you describe does not appear for me. I am on Firefox 66.0.3. My addons are still not available.

  9. Rick Tillery wrote on

    How about some love for mobile FF users!? Our add-ons were disabled too!

  10. Phillip wrote on

    About:studies lead to nothing.

    Version 66.0.3

  11. Arundel wrote on

    I have just come across this post as ALL my add-ons have just disappeared, and listed as ‘unverified’ by Firefox.
    I am unable to use my password manager (add-on disabled by Firefox).

    I have enabled Studies as per above and am waiting to see if/when the fix is active.
    Still waiting…
    About:studies still reads “prefflip-push-performance-1491171•Complete”

    Firefox 66.0.3 (64-bit)

  12. Jonathan wrote on

    The option to allow studies to run is not available for Firefox on Android. How do we deal with this issue for that version?

    1. Kev Needham wrote on

      A separate update for Android that corrects the issue is being prepared. We’ll update the post and on social when it’s available.

      1. Jonathan wrote on

        Thanks for your efforts. Fix worked perfectly on my windows machine after I restarted the browser.

      2. Ruca wrote on

        While you’re at it, please integrate text reflow for Android. Before you think that you are finished, look at how well it works on Opera Android. Thanks.

      3. Myles wrote on

        3 hours later and still nothing. Can you please respond with an answer that isn’t a canned corporate response, and tell us EXACTLY what you are doing to help us and WHEN it will be live? Also ideally without a 6 hour window where it won be fixed but you tell us it is fixed, despite nothing having changed.

  13. Alex wrote on

    Seems working fine, just need to restart firefox after anabeling the data collection/studies

  14. Charles wrote on

    I show the hotfix as active, but plugins are still disabled.

    Running Ff version 66.0.3 (64-bit)

    1. Charles wrote on

      Meant to say add-ons are still disabled

      1. Charles wrote on

        This study sets app.update.lastUpdateTime.xpi-signature-verification to 1556945257.

  15. Chris Reynolds wrote on

    about.studies not opening anything.
    When are these issues going to be fixed?

    1. Kev Needham wrote on

      enter “about:studies”. The fix is live, and should propagate to your installation within six hours.

    2. Flash wrote on

      same here about:studies displaying a blank page
      addons still disabled

      66.0.3 64-bit win 10

  16. Charlie wrote on

    Ok on Windows 10 platform/ Still waiting a fix on the android version.

  17. Todd H wrote on

    About studies shows: “hotfix-reset-xpi-verification-timestamp-1548973•Complete”
    All my extensions are still disabled. Using version 66.0.3

    What’s up?

    1. Kev Needham wrote on

      The study that corrects the issue isn’t loaded. There is a second fix that can take up to six hours to load, and is named “hotfix-update-xpi-signing-intermediate-bug-1548973”.

      1. dtickmd wrote on

        “hotfix-reset-xpi-verification-timestamp-1548973” is currently “active”.

        Not seeing “hotfix-update-xpi-signing-intermediate-bug-1548973” at all. Does the 2nd fix not even start to load before the first is complete?

  18. Andreas wrote on


    Addons are back.


  19. Igor Jerosimić wrote on

    It worked, but I had to enable data collection and studies.

  20. TERRY M wrote on

    Version 66.0.3 (64-bit)

  21. Gary wrote on

    it’s active in mine but it’s still not fixed. Firefox version is 66.0.3

    1. Kev Needham wrote on

      Please ensure that the “hotfix-update-xpi-signing-intermediate-bug-1548973” study is active. There is a second, similarly-named study that is related, but doesn’t correct the issue.

      1. Gary wrote on

        once I clicked send, the problem was resolved about 60 seconds later!

      2. Jannette wrote on

        I do not see the hot fix update on about studies i am seeing P prefflip push performance as active. Thats it. Nothing else this is not very nice

  22. Jayson wrote on

    Sync looks live it is still not working for me. I have version 66.0.3, in about:studies I have listed in the completed studies:
    This study sets app.update.lastUpdateTime.xpi-signature-verification to 1556945257. Not sure if that is the right one or not, and if I still have to wait for another of to fix the problem with adding add-ons and for my old ones to work?

    1. Kev Needham wrote on

      This is not the study that applies the fix. “hotfix-update-xpi-signing-intermediate-bug-1548973” is the study that applies the certificate fix.

      1. Jayson wrote on

        okay, so nothing is showing up in active studies and I do have fire fox allowed to install studies checked off so I take it I just have to wait till the system fixes the problem?

  23. Karsten Spies wrote on

    Both studies active, addons still disabled 🙁

  24. GabiGKG wrote on

    dom.push.alwaysConnect was setted to “true” in abot;config. Add-ons are STILL DISABLED. When is this going to be fixed ?
    My Firefox latest Version is Firefox Quantum 66.0.3 (64-Bit).

    1. Kev Needham wrote on

      It can take up to six hours for the study to load and be applied.

      1. aswiran wrote on

        6 hours since connected to internet or 6 hours as long as it connect to internet?

      2. Ket wrote on

        How do we go on about it on Android?

      3. JFC wrote on

        Kev, six hours from WHEN Pacific Standard Time?

        In other words, by what time PST should users expect to have received the fix by?

      4. GabiGKG wrote on

        Bug is fixed – addons are downloaded – thanks!

    2. GabiGKG wrote on

      Bug is fixed – addons are downloaded – thanks!!

  25. Jim Darroch wrote on

    Studies is not an option in my old laptop which is running FF 52.9.0 as it’s on XP. Does this mean that Mozilla have now withdrawn FF for XP users?

  26. David wrote on

    Still having this issue after fix had been applied I am on FIrefox 66.0.4 64 bit

    1. David wrote on

      Studies Active are:

  27. P wrote on

    In Firefox 60.6.1esr there is no “studies” option to select in preferences!

    What to Do?

  28. Dermeg wrote on

    My plugins were disabled after a popup appeard on asking me to disable AdBlocker.

  29. Karsten Spies wrote on

    Oh, sorry… After 2 restarts of Firefox my addons are back again 😉

  30. James Dening wrote on

    My two important add-ons — Emsisoft Browser Security and RoboForm Password Manager were disabled in Firefox 66.0.3. In trying to fix this, I made the mistake of removing one of the add-ons that were disabled. At this point, I can’t re-install either one of them because I get the Red Message, “Download Failed. Please check your connection.” I have had to make Google Chrome my Windows 10 Home “Default Browser” because of this problem created by Firefox Quantum. I sure don’t understand Firefox’ disabling these two very important add-ons and I hope this gets fixed soon so I can download and install and/or re-enable either or both of these add-ons!

  31. Bill F wrote on

    This bug has disabled my Lastpass addon where I manage over 250 random generated passwords for various sites using all character types and very long passwords. This is NOT cool. I hope this Studies thing fixes the problem. I await the fix. I hope it comes soon and is effective. I have used Firefox for many years and this bug is unacceptable. Fix it soon!

  32. Keith Nichols wrote on

    Am I correct in understanding that if we wait long enough, FBP can again be installed from the FBP website in the traditional way as if the current kerfuffle had not taken place?

  33. Kaban wrote on

    I am using FF 56. The fix is there, but extensions are still disabled. How do I get my extensions back? Switching to a higher FF version is not an option because some critical legacy extensions are simply not there.

  34. Mauro Torrez wrote on

    Firefox doesn’t let me enable the setting “Allow Firefox to send technical and interaction data to Mozilla” or “Allow Firefox to install and run studies”. They’re both grayed out :(. Running 66.0.1 from Debian unstable package.

  35. BB wrote on

    If use FF 60.6.1 ESR on Debian stretch stable.
    There is no “Allow Firefox to install and run studies” option.

    What can I do?

  36. Xavier wrote on

    Hello Mozilla,

    This has reached Tor Browser also : HTTPS Everywhere and NoScript, are just gone.

    Is there any workaround via “about:config” ?


    1. Xavier wrote on

      Sorry I was not accurate here :

      * HTTPS Everywhere is still here and appears to function , but an update if offered and fails to install. Note, it is dated from year 2000.

      * NoScript is disabled entirely, as I wrote.

      * Ublock Origin is disabled, also. This one is not bundled in Tor Browser by Tor Project, but was installed manually on top of it, therefore this is less surprising. Note, I have seen it preinstalled in Tails and I believe it is popular with Users of Tor Browser.

    2. Xavier wrote on

      Finally, this just reached also Firefox ESR as installed from Debian stable repositories, just like with Tor Browser here :

      * This occurred all of a sudden, in the middle of a session i.e. without even restarting the browser.

      * These buidls do not include any « studies » feature, either.

      Any workaround, please ?

  37. Karthik K wrote on

    Hello all. We are running Firefox v61 in an enterprise configuration with managed add-ons installation using Windows registry. Everything was working smoothly until the add-ons bug hit us. We have tried using the “studies” approach and it is not working for us. Restarting Firefox doesn’t automatically fix the add-ons installation. Will the more general fix automatically work for older versions of Firefox?

  38. Bill F wrote on

    By the way I am on Firefox 66.0.3.

  39. Fortune wrote on

    Still no fix. Studies are enabled

  40. Alexander Brüsch wrote on

    What about Android Firefox?
    I have the same issue on my phone.

  41. m goto wrote on

    What kind of update should we look for if we are on the esr update channel?
    Should we consider switching to the release channel and then switching back at a later date?
    Thanks for any advice or recommendations

  42. Dieter Kuckelkorn wrote on

    What about Android users? Will there be a solution as well – apart from switching to Chrome?

  43. skwabie wrote on

    Does this fix apply to legacy Firefox 56.0 and before?

  44. John Mauer wrote on

    All addons have been removed at approx 10:50 a.m. EST What gives

  45. Bruce Murray wrote on

    Allow studies option will not stay checked

  46. Aaron wrote on

    Studies are on, applied, and addons seem to be working again. Thanks for the quick action.


  47. Sergey wrote on

    But what about FF ESR (52.9.0) ? – there is NO studies option

  48. Sylvie Bodineau wrote on

    Nothing fixed yet on my side. HTTPS everywhere, ublock, zotero connector, java script, hola fix vpn, and others… all disabled since more than 12 hours

  49. Haversack wrote on


    I am on an esr channel on one machine, using 59.2.0, 32-bit. Studies doesn’t exist for this version as best as I can tell. Will a fix come for these older installs?


  50. Derdada wrote on

    Firefox ESR does not have the option “allow firefox…. and run studies”

    Using ESR because we need a stable system – but now its more unstable than mainstream firefox! 🙁

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