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. Rob wrote on

    Running Firefox 52.9.0 ESR (this hardware won’t support an OS upgrade), and was affected by this change. I thought the ESR channel wasn’t getting any more changes – why was I affected to begin with? And when will I get my add-ons back?

  2. sweetpea wrote on

    Thanks for fixing this so quickly. My add-ons are up and running again. <3

  3. William wrote on

    Firefox still not accepting the add-ons.

  4. 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?

  5. mpppp wrote on


  6. David wrote on

    When will the general fix become available?

  7. RaanMavi wrote on

    Everything is fine here.

  8. Mukesh Kapoor wrote on

    I have version 66.0.3 and I still can’t install after following the instructions.

  9. Jane wrote on

    I’ve just got a pop-up that my add-ons got disabled. I’m using Firefox ESR 52.9.0 [my computer is old and it’s the latest release of Firefox that works on it, so no update advice please cause it won’t work for me]. How can I get my add-ons go back to work? This entry tutorial doesn’t work for ESR release.

    1. Andrew Koster wrote on

      First time I’ve seen a pop-up ad in years (decades?). This is really going to erode trust in Firefox.

    2. ESR wrote on

      me too.

      this sucks big time!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  10. mik wrote on

    This solutions doesn’t work on Firefox 66.0.3 on Fedora 29.

    I checked ths box in preferences and I see nothing in about:studies after 2 hours.

    I had to install the certificate manually.

  11. eliott wrote on

    This is really frustrating. First you make changes to the type of themes the browser can handle, which affected the one I use, and now this, all my addons have gone and I can’t download replacements. Come on folks!

  12. I Z wrote on

    Same here on Firefox 66.0.3 (64-bit) MacOS.

    Tried setting the app.normandy.run_interval_seconds to 5 seconds to try to speed up the deployment of the studies, but I’m only getting the hotfix-reset-xpi-verification-timestamp-1548973 and not the hotfix-update-xpi-signing-intermediate-bug-1548973.

  13. Greg wrote on

    Under ‘Completed studies’ Had the following on 2 different computers:

    This study sets dom.push.alwaysConnect to true.

    This study sets dom.push.alwaysConnect to false.

    I did get the addons working again on both computers – but, I had toggled the one with true to false and then changed it back to true to get the addons to work. So what is the secure setting, true or false? Why was there a different setting for what appeared to be the same hotfix for two different computers?

  14. kwyxz wrote on

    The option to enable Studies is greyed out on my browser, lmao.

  15. Ohachiyo wrote on

    It’s working for me on 67.0b16 (64 bits). Keep up the good work!

  16. Illia wrote on

    Firefox 66.0.3 (64-bit)
    hotfix-reset-xpi-verification-timestamp-1548973 active

    Add-ons are still disabled

    1. Tzunamii wrote on

      Same for me.

  17. DR wrote on

    Using FF56.0.2 still no fix yet? Thankfully I had backups of FF profile and was able to restore.
    I feel sorry for those folks without backups.
    Not a good situation Mozilla, allow us old version users to turn off addon verification, please!

    1. Namari wrote on

      DR, how did you restore? I have my profile folder backed up but that doesn’t seem to help solve anything.

  18. Dat Gurl wrote on

    Why do we have to enable allow studies, and when will be able to untick the allow studies box once you’ve “fixed” the problem. It seems unfair that we have to allow studies and have our data collect all because of a mistake made on your end.

  19. Rodolphe wrote on


    I am using FF 65.0 provided by my organization with the add-ons disable and studies also disabled and not changeable (probably because my “organization has disabled the ability to change some options”).

    What could I do to reactivate the add-ons?

    Thanks in advance.

  20. Andy wrote on

    I am running an older FF ESR 52.7.2 (32-bit) on a Windows Vista machine and have automatic updates turned off. I have 50+ add-ons and a dozen of them have suddenly become disabled without an update occurring.

    Firefox Options/Preferences -> Privacy & Security -> Allow Firefox to install and run studies is not an option in my version of FF. About:Studies is not running on my version and just gets a “Address isn’t valid” page.

    I purposefully did not let updates happen because my add-ons are not going to be re-developed for the new, “we don’t care what our users want” version of Firefox. If I update, I will lose most of them. The weird part is that some of the ones disabled are newer, like LastPass and Kaspersky, which have been re-designed for the new FF.

    Is this some backhanded way to force older versions to stop being used and force FF users onto the new platform? How will mine be fixed if I can’t run the studies?

  21. Nerida wrote on

    For anyone concerned about having to share information with Mozilla in order to receive the hotfix, please re-read the original post, specifically:

    “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.

    … We are working on a general fix that doesn’t use the Studies system and will keep this blog post updated accordingly.”

    tl;dr – when your add-ons are working again after getting the hotfix, you can disable Studies again.

  22. PD wrote on

    Okay, I did something stupid and accidentally clicked “remove” on the studies page. Is there any way to change that back?

  23. sad firefox user wrote on

    enabling the studies solved the issue faster than I thought considering it might take up to 6 hours
    my problem is now that all settings have been erased of my Firefox Multi-Account Containers addon

  24. Ryan wrote on

    The fix seems to have worked for me after using the suggestion to change the intervalseconds setting to a low number. Of course, many users wouldn’t know how to do this.

    To me it’s unacceptable that with an issue of this magnitude, you are okay with simply stating it may take six more hours for the update to be applied. It seems to show a lack of recognition of the severity of the problem on the part of Firefox.

    This has been my browser of choice but I will definitely be reconsidering it.

    1. Andrew Koster wrote on

      You’re right, everything about their handling of this situation seems to show a lack of recognition of the severity of the problem. It took almost a day for them to make the fix available at all, it’s a temporary fix, and it still isn’t working for some people.

      Why is there even a certificate issue in the first place? If an SSL cert expires on my website, I can renew it for free and it takes about 10 seconds. I’m just some random dude. Why does it take all of Mozilla an entire day to sort-of resolve a catastrophic failure in a feature that users should never have even noticed?

  25. Henry VU wrote on

    To all the guys out there saying the fix is not working

    1) Apply the fix as said.
    2) Close Firefox and make sure it is not run in background by checking taskmanager
    3) Re-open Firefox
    4) Wait around 5 mins or so, your addons will auto reappear

  26. Neil wrote on

    The study appeared and all my add-ons are functioning again. Thanks.

  27. Sue wrote on

    One trick said to work is to set the date on your computer to a few days ago, before the expiry date of the certificate. I am also on 56.0.2 because of needed legacy add-ons. Almost all my add-ons are disabled even some installed by Mozilla itself!

  28. Ardnaxela wrote on

    So, if I’m one of the unlucky ones who’ve always kept studies disabled, I can expect up to 6 hours for studies to be applied? I can’t quite make out whether the three studies I see as completed in the ‘about:studies’ response pane mean it’s running already and the fix’ll be applied soonish.
    The internet is a complete hellscape, guys.

    1. still me wrote on

      Uhh, so, I see my previous comment as ‘awaiting moderation’ but everything’s been fixed, on my end – refreshed a page just for the sake of it and BAM – addons back on. Checked about:studies, and sure enough, I’ve got the fix. For reference: using FF66.0.3, so the current version, which, as luck would have it, I had just updated today. Glad to see the firefox team working so hard. Thank you guys!

  29. Alice wrote on

    The theme thing still does not work. However, I am glad that you guys are on this and are working hard to get things back to normal.

  30. Gordon Whitehead wrote on

    “A substantial update in the coming days” – a rather leisurely approach to what is a major problem by all accounts and a problem that shouln’t have arisen in the first place from what I have seen on the internet . I have enabled Firefox Studies with some reservations, so hopefully sometime within the next six hours or so I’ll be able to do what I set out to do some eight hours ago. But then again…..

  31. mge wrote on

    Nothing (still) happening here. No fix. No “hotfix-update-xpi-signing-intermediate-bug-1548973” in the studies and no Add-Ons.

    Sounds like I’m heading over to one of the many other browser options. Maybe I’ll try Firefox again in the future.


    1. Caroline wrote on

      Am thinking the exact same thing – what is going on :(((((

  32. anon wrote on

    Yep. Some addons stop working. This is how you lose users. Mozilla was such good browser.

    1. Caroline wrote on

      Me too.

    2. Andrew Koster wrote on

      It’s not some add-ons that stopped working. It’s all add-ons, from what I can tell, or a least a vast majority. All of the ones I had installed, all of the ones that MOZILLA OFFICALLY RECOMMENDS for ad-blocking, they all broke.

      All of the security features come from the add-ons! Give me an unsigned add-on, and let it actually run, that’s a lot safer than running a million pieces of garbage tracking code and pop-up ads!

  33. mik wrote on

    Ok I see them now.

    Can I stop the studies now ?

    I have this one too: prefflip-push-performance-1491171

    I don’t know what it does but I hope It breaks anything, I am interesting to suppress this another study, if it’s possible.

  34. Jeff Cooper wrote on

    When AdBlock went down yesterday I thought “WTF?” when I tried to reinstall it and failed I thought “WTF?” again. the number of WTFs have grown… although AdBlock is back now. So yeah… you guys have fixed the problem… but… you’ve been very minimal with your explanation about *why* this happened in the first place.

    Was Firefox hack attacked? As a number of comments here indicate the idea of having to share more personal info with Mozilla seems a bit hypocritical since you haven’t been exactly forthcoming with info yourselves. It’s like Facebook selling our private info but then suspending my account for 3 days cuz I said “some men are pigs in the bathroom” (saying it was hate speech).

    I have always used Firefox; I expect a more complete explanation soon.

  35. Vitaly wrote on

    Why there is no explanation of the root cause?
    Is this is a bug? a mistake made by FF devlopers?

    1. Caitlin Neiman wrote on

      This is due to an expired certificate in Firefox.

  36. midimax wrote on

    Unfortunately does not work here.

    German language 66.0.3 64-bit, studies was activated and showed hotfix-reset-xpi-verification-timestamp-1548973 active, but all Add-ons still disabled due to “not verified”.

    1. midimax wrote on

      Okay i see the study should have a another name, my fault. Forget my post seems i have to wait longer until i get the correct.

  37. Tony Quan wrote on

    Hi, on Linux Firefox 66.0.3 I’m only seeing the hotfix-reset-xpi-veriification-timestamp-1548973 study, and not the hotfix-update-xpi-signing-intermediate-bug-1548973 study. I know that the latter is needed to actually fix the issue. Has this gone out for Linux?

  38. Uh-huh wrote on

    “bug” causes privacy addons to dissappear. Release “fix” that makes you enable data collection. Yeah this isn’t suspicious at all.

    1. Curious wrote on

      …and why is that? Just curious

      1. Andrew Koster wrote on

        Everything about this situation is extremely weird. I don’t think there’s anything malicious going on, but I’m surprised to see them drop the ball this hard.

  39. Eric M wrote on

    The studies showing up in that tab for me:

    Are both labeled as Completed studies in my studies tab. My addons are still disabled after this.

    Currently using Firefox Quantum 66.0.3 (64-bit)

  40. BarbS aka BeingAngry wrote on

    Thank you so very, VERY much for this fix. I have used every version of Speed Dial since the first one and it is such a great help for someone like me who thumbnails the pages I use most often and who also bookmarks many other pages for research. It is such a distress when everything I use disappears and I do not know where the backup is stored on my computer. Google is more than annoying for me and I do not appreciate the way Google tries to force everyone to use its browser. Firefox has been the BEST experience for me and I do so appreciate the Free and Open Browser. Thank You! Your Team is awesome!

  41. muttbob wrote on

    Thank you Firefox team. I enabled studies, restarted, add-ons still not working. Clicked on find an add-on that works in “about:addons”, and as soon as the add-on page loaded, all of my add-ons came back on. I had only used Firefox to search for a solution since they shut down last night, but now I can use it for everything again.

  42. rsm wrote on

    On Slackware Linux Firefox comes without data reporting! “Data reporting is disabled for this build configuration”. So no, there is no fix. You nuked remotely our browsers and now you ask me to wait _DAYS_ for more information and maybe some fix? And you want me to browse the Internet until then using what? Chrome?

    It would be great to read any sort of apology. But no…

    1. Andrew Koster wrote on

      Yeah, it’s crazy how there are all of these hacky workarounds and that’s supposed to be OK, when everyone knows that they can easily just switch to Chrome and avoid the nonsense. Some recognition of how bad this is for Firefox, at least an “oops, we did a bad thing” from an official account, would be nice.

  43. now very pissed off wrote on

    So how long am I expected to wait to have this hotwire of a fix work on the latest version of FF because its already past 11 central here and all my stuff is still broken and I am very mad that i have to spend my saturday morning looking for new browsers instead of being able to get stuff done

  44. Karthik Krishnamurthy wrote on

    In light of the new add-ons issue, what would be the fate of enterprises running older versions of Firefox? Our organization runs thousands of Windows systems with Firefox v61 with a managed add-on installation
    using the windows registry method. How is the fix for these older systems going to arrive for the add-ons bug? Do we have to manually update the Firefox versions or install some system add-on or are things going to start working automatically?

  45. MadDog wrote on

    Ok, I found the problem. Somehow, my default profile was corrupted. If you go to about:profiles, click on create new profile, select the new profile and click on make default, exit and restart Firefox. Now, you should be able to install whatever add-ons you need to.

  46. Mark Roth wrote on

    I have tried to activate studies, however it does not remain active. Once I close the options tab, studies are disabled again. When I check view studies, it says “No new studies will run”

    1. Bill Meahan wrote on

      Same problem here. Linux Mint 18.3, Firefox 66.0.3

      Great way for Mozilla to lose yet more marketshare to Chrome.

  47. Xavier wrote on

    OK, on both Firefox ESR from Debian stable and on Tor Browser from Tor Project :

    Setting “xpinstall.signatures.required” to “false” in “about:config”, does instantly re-enable addons : they are working again, a warning is displayed for each in the addon list.

    I’d suggest to FIRST disable addon auto-updates and UNTILl this problem is solved.

  48. DavidGB wrote on

    I am mildly intrigued as to why my FF 66.03 (64 bit) has been working fine, all 33 installed plugins present and correct and never disabled, throughout this whole affair.

  49. Daniel Wilkins wrote on

    My biggest question related to this incident is pretty simple: how could this have happened in the first place? I completely understand being unable to install *new* addons, but why is Firefox (I assume) phoning home to “verify” that known-good addons are still good? Why was this system chosen rather than, say, keeping hashes of your installed addons and only checking if the hash changes or if the addon is updated?

  50. Ed Only wrote on

    I’d like to thank Mozilla for making most of the sites I visit intolerably ad-infested, enough to prompt me to go outside and work in the yard instead of wasting my time arguing with strangers on the internet. I’m serious. OK, bye.

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