Latest Avast reportedly deleting Firefox add-ons

Martin Brinkmann
Nov 16, 2014

Several locations on the Internet, including the official Avast forum, Reddit and Firefox support site Mozilla Zine, are filling up with user reports that that latest version of Avast deletes Firefox add-ons automatically.

Some users report that add-ons get deleted automatically on startup and without option to prevent this from happening in the first place.

The issue does not seem to be linked to the program's Browser Cleanup tool directly even though it is designed to detect and remove lowly rated plugins and browser extensions that are installed in popular browsers such as Firefox or Internet Explorer.

It is unclear right now what is causing the issue and why only some users of the browser who have Avast installed on their systems are affected by the automatic removal of Firefox add-ons on the system.

Here are user comments about this taken from various sources:

The add-ons are deleted automatically, not via  browser cleanup tool and there are no reports of malware being detected. I witnessed it happen "live" as I was in my add-ons manger list, add-ons being removed automatically.

I can confirm this too. Since the last program update Avast removes half of my firefox addons automatically on every system startup

Huh. That happened to me earlier today too. The catalyst was updating FF from 33.1 to 33.1.1. When FF restarted itself after updating many of my addons were missing.

The issues are confirmed by some users but not noticed by others. The only common denominator is that all affected users run the latest Avast on their PC and use Firefox stable.


Since it is unclear what is causing the issue exactly, it is recommended to backup your Firefox profile just in case. You can use a program like MozBackup for that which is provided as a portable version and installer.

All you need to do is run the program, select the version of Firefox that you want to back up (it supports portable installations as well), select the Firefox profile to back up, and then what you want to save to the local system. Make sure that extensions are selected.

Now You: Are you running Avast and Firefox? If so, did you notice any issues?

Latest Avast reportedly deleting Firefox add-ons
Article Name
Latest Avast reportedly deleting Firefox add-ons
Reports have surfaced on the Internet that the latest version of the security tool Avast deleted Firefox add-ons on some systems.

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  1. Alec West said on May 7, 2015 at 9:38 am

    Removed by user.

  2. Omega said on November 19, 2014 at 11:02 pm

    Time to get away from Avast. This isn’t the first time they made a terrible mistake.

  3. Ficho said on November 17, 2014 at 5:58 pm

    lukor (Avast team):
    Hi guys,
    thanks to all for the information posted. We have been able to identify the problem now. Browser Cleanup is responsible for this issue. A bug in the component calculating hashes of the extension packages cause (only in some rare cases) deletion of the wrong file – the original instead the packed one.

    Sorry for that and thanks again for your help obtaining the repro steps for us.

    The Browser Cleanup team is now working on a fix, which will be delivered via a VPS update shortly (tomorrow).


    1. Zipko Entrails said on November 17, 2014 at 11:51 pm

      Lukas of Avast,

      I have to say, this bug has caused me hours of lost productivity. I lost all my Firefox add-ons, and came to believe I must have a virus and spent the afternoon scanning for malware. I am going to have reinstall my add-ons (assuming I remember which ones I had), and reconfigure Firefox. Most of us who use Firefox have it heavily customized and it represents a real loss in productivity when the browser is not configured the way it normally is.

      I basically lost a day’s worth of work chasing after this problem until I figured out from Google searches that Avast was causing it. Great. My AV is screwing up my life.

      I am actually someone who has purchased Avast, and who also uses the phone app.

      You know what I’ve spent the last half-hour of my wasted day doing? Searching for good alternatives to Avast — and there are several to choose from.

      Everyone makes mistakes, but this is frankly a pretty bad one — the program I use to protect me from viruses and malware essentially behaved like malware. My faith in your product is seriously shaken.

      1. Charles Robinson said on November 18, 2014 at 4:41 pm

        So – is Avast going to field a fix? When?

    2. pschroeter said on November 17, 2014 at 6:13 pm

      So I deserve a free upgrade from the free version for my trouble, the panic, and several hours of work I have been through?

    3. Martin Brinkmann said on November 17, 2014 at 6:02 pm

      That’s great news Ficho, thanks!

  4. TTTB said on November 17, 2014 at 12:57 pm

    I think this issue does not exist yet in Pale Moon because of its derived (with major edits) codebase.

    The three most common addons reported as removed on the three linked threads are Classic Theme Restorer, Open With, and Adblock Plus.

    Avast has been slightly buggy in recent times…

    1. Dieu said on November 19, 2014 at 9:34 pm

      PM has it’s own serious issues with Major Add-ons being unsupported like ABP… ;-)

    2. Mike J said on November 17, 2014 at 1:58 pm

      I also have not seen this issue with Pale Moon or Waterfox, which I use because of the gmail problem in Pale Moon.

  5. Goodwill said on November 17, 2014 at 10:13 am

    I think I’ve found the solution : after installing Avast 2015, open Avast user’s interface and click on browser cleaning. Once the cleaning is done (actually there’s nothing to clean since most addons have already been removed), click on the Mozilla Firefox button on the left and check the option “exclude addons which have a good reputation”.

    1. Charles Robinson said on November 29, 2014 at 12:42 pm

      I found that “exclude” box check-marked already – and I did not do it.

    2. Tommy said on November 17, 2014 at 6:18 pm

      Thanks Goodwill, your solution worked for me…

  6. Ken Saunders said on November 17, 2014 at 9:31 am

    Wow, this is all surprising.
    I usually stay on top of keeping programs updated, but I did stop doing so with Avast for pretty much the same reason that firefoxlover said so I’ve been able to avoid this issue.
    Their new program updates became pretty destructive and would cause major problems for me, so I usually wait a while before updating and then end up doing a clean install which is a wicked time consuming pain in the azz to do but necessary.

    They need to do a better job at testing things thoroughly across all browsers and platforms before calling something a final release.
    There have been issues with Avast messing up things for Firefox users in the past and considering how serious and widespread this issue is with Firefox users, I wonder how many devs even use or test with Firefox.

    They should be offering incentives and encouraging their massive user base to engage in testing instead of using all of their user base to do so and they should use Bugzilla like Mozilla, WebKit, and many others do.
    I wonder if like other companies, etc, they hire/assign a new person to new components added to their products, or they just add something new and it becomes the 12th responsibility of one or two people.

    I like Avast at its core (I don’t like the 80 other things), and I’ve used it for I guess 8 or 9 years and I’m not ready to just dump it, but I’ll look into Avira just to have something ready if I decide to make a change. They’re support forum and volunteers have been helpful and quite good and I still trust it.

    I’m wondering if someone can answer this for me.
    Since the virus definition base is constantly updated, how often do I really need to update the program itself?

    About backing up Firefox.
    MozBackup and FEBE are great tools for selectively backing up things, but I just copy the/a whole profile folder and put it in a safe place (usually a different storage device) and restore to it if I need to.
    I’ve done this after catastrophic system or other failures for both Firefox and Thunderbird and I’ve done this when traveling. I just put my profiles on a portable drive and point to the location on whatever machine I’m using (like at someone else’s house).
    So you create a new Firefox profile > “Choose Folder” > select the profile you’ve backed up.
    Of course using Sync or keeping the folder synced or backed up frequently is a good idea.

    1. Dieu said on November 19, 2014 at 9:37 pm

      I use Avira Free too but I use the Version 12 (2011 version) which is lighter than current version.

      I tweaked a bit Avira and don’t see any ads to upgrade or message, the power of an antivir is it’s database and mine is updated everyday.

  7. stilofilos said on November 17, 2014 at 6:01 am

    I bade farewell to that avast years ago after it had even managed to kill itself in two consecutive clumsy updates in four months… (the first time I surmised that windows’ instability possibly having caused its crash, and I reinstalled it)
    It had also blocked reinstall of my firewall (first Zonelabs when that one was still lovely, AVS afterwards) and Malwarebytes.
    And that was more than enough for me…

    Apparently it still does not fare that well…

  8. infogain said on November 17, 2014 at 5:54 am

    thats why i don’t use avast web shield.
    just file shield only.

    1. Pants said on November 17, 2014 at 2:25 pm


      For the record, I always do a custom install, and uncheck the bloated crap such as browser addons, grim fighter, software updater etc. Furthermore, I used to have it automatically check and tell me about program updates – but now silenced that about a year ago. Been using avast for about 3 years. Its been on my shit list for about the last 18 months.

      About 18 months ago a product update with some major core changes ending up borking web traffic – there was bitchin’ galore in the forums and on f**kbook. After three or 4 hours, I eventually found a “fix” – editing an ini file that disabled the new “engine/method” and renabled the old one. Result – I always wait a month before updating.

      About a year ago, another update absolutely munted (that’s slang for completely fucked and garbled) my web traffic and that of a couple of my clients. What we had in common is portable Firefoxes. For some reason, clients with installed Firefoxes had no issue. Result – turned off web shield.

      Another change about 6 months (i think) ago totally screwed with my portable thunderbird’s TLS/SSL. Still does to this day by injecting itself as a digital signer or something. Result – turned off Email Shield. I don’t have any qualms – my machine is clean for outgoing, and my settings and my own common sense is too smart for anything incoming in mail.

      Now I see Martin posting about their stupid browser addon (which i have never installed or allowed) being ass-holey and injecting crap and wasn;t their some rumbling about them aggregating data on users, and something else about demanding your first born. And now this bullshit screwing with people’s setups, wasting everyone’s time.

      TL;DR: Avast was ok 3 yrs ago. Now with everything omitted in installs and everything but file shield turned off … and product updates set to manual and never actually done … I now await file shield to try and fuck with me. :)

      PS: Personally, I consider AV to be about the 20th item on my list to secure a machine, but still essential as a last line of defence.

  9. InterestedBystander said on November 17, 2014 at 3:29 am

    I dropped Avast after it blocked #Develop from running. Switched to Avira. But I use Linux 95% of the time anyway.

    The co-evolution of malware and anti-malware programs is interesting to watch. Personally, I don’t think malware programmers are going to become either less sophisticated or less persistent over the next few years — quite the reverse — and so I expect continued escalation. Sneakier, tougher malware; more controlling and intrusive anti-malware.

    To it’s credit, Microsoft recognizes the problem (“…we are facing not an evolution in malware but a revolution”, one spokesman said) and is attempting with Win 10 to transition to a sort of sandbox model with apps, to build a repository of trusted applications, and institute stronger user authentication. But I’m not sure if these measures will outpace malware development enough to make a difference.

    1. Oxa said on November 17, 2014 at 8:34 pm

      The problem isn’t how sophisticated the anti-malware software is, but how paternalistic it is. Sophisticated algorithms are fine as long as the user remains in the driver’s seat to determine if, when, and how the algorithms are used.

    2. Jan said on November 17, 2014 at 8:32 am

      However these measures guarantee the definitive loss of liberty user side. gg

      1. InterestedBystander said on November 17, 2014 at 3:20 pm

        Agreed. Under the umbrella of “enhanced user security” Microsoft will probably sneak in a lot of semi-mandatory registration and user tracking measures as well — even more than they already have done, I mean.

  10. pschroeter said on November 17, 2014 at 1:50 am

    Hello, I’m the guy who made the post on the Avast forum you link to in the first sentence.

    I’m still fighting with Firefox and Avast over what add-ons I am allowed to have installed. I am reasonably sure the problem is caused by Avast being overprotective, because its name keeps coming up in the Avast and Firefox forums I have posted my problem in.

    Friday night I grew tired of waiting for a clear answer in the forums and started reinstalling many of my add-ons and things were pretty much back to normal because it seemed to have left my add-on preferences intact. The next day I found Classic Theme Restorer deleted again, but it for some reason it left the others I had reinstalled alone.

    Yesterday I grew frustrated and decided just to see if I could get use to the new interface and live without Classic Theme Restorer. Things are moved around a little, but it isn’t completely awful and I am getting sick of fighting with how Mozilla wants me to do things. I even installed a new add-on to bring back the only thing I really miss, the status bar. I was thinking I could live with the new interface, then found today the few add-ons I installed yesterday were missing taking with it the status bar. And it still left add-ons it deleted two days ago alone.The battle continues and I worry about when and what will turn up missing next.

    1. Dieu said on November 19, 2014 at 9:29 pm

      Whay U don’t just change Avast for another free Antivir ??? Worst just change to Avira Free for few weeks the time Avast pick up on the issue… ;-)

  11. Ahmed said on November 17, 2014 at 12:05 am

    Just happened to me here.

    I got the Avast popup saying a new program version was available, updated and restarted and my add-ons started disappearing. I didn’t do a browser cleanup or anything like that.

    Luckily, I regularly save a backup copy of Firefox. I restored my Firefox, turned off browser cleanup in Avast for good measure and so far, my add-ons are staying put.

  12. Neal said on November 16, 2014 at 10:34 pm

    Really the only thing you need from Avast is the realtime protection shields, and maybe NG. All the other stuff including browser cleanup are half baked tools.

  13. michaelpaul said on November 16, 2014 at 9:09 pm

    Enough with avast ,detection rates suck anyway
    IL give panda a shot as i know others have panda and
    speak highly of it ….

  14. Sven said on November 16, 2014 at 8:09 pm

    Sometimes it is really great to be on Linux. No need to mess around with such issues…

    1. anon said on November 17, 2014 at 10:14 am

      Yeah, there’s already a whole lot of other issues to deal with there.

      1. ns said on November 29, 2014 at 5:10 am

        Lol, quite true.

  15. souldances said on November 16, 2014 at 6:53 pm

    Lost my Firefox extensions after starting Avast Browser Clean Up, then stopping after reading the warnings about what it would do. Was going to remove the one low-rated extension in Firefox rather than let Avast have its way, or so I thought… Pretty pissed at Avast now – think it’s time to look at other anti-virus options.

  16. firefoxlover said on November 16, 2014 at 6:15 pm

    I always wait a while prior to updating Avast program to be sure that all kinks have been addressed and corrected. Sounds like they’re biting off more than they can chew. Reading their forum is a big help to see if corrections have been made or not and what the problems are. Avast has to focus on what they do best, being an antivirus program and nothing else. Who wants all those added bells and whistles that have been added in the last few years? Not me so I always do a custom install and remove, untick the boxes of features that I don’t want. Hands off my Firefox Avast! So I probably wait until next year to update if all problems have been fixed. If not they will have lost a customer since version 4.8

    1. Oxa said on November 16, 2014 at 8:27 pm

      Two thumbs up! My sentiments exactly.

  17. Stevey said on November 16, 2014 at 5:13 pm

    I noticed this after I had to stop quick scan from finishing part way through. All my extensions got deleted, apart from LastPass. I ran browser cleanup before I ran quick scan, but it didn’t find anything to remove. I thought it was me halting the quick scan that had caused it to happen.

  18. Lookmann said on November 16, 2014 at 5:06 pm

    Time to get away from Avast. So far so good , buddy. But you’ve overgrown. Bloated beyond belief.

    1. Seban said on November 16, 2014 at 6:02 pm

      I used Avast for many years up until version 2014. Then I switched to Avira Free Antivirus.

      Avast added too much stuff I don’t need and readded this stuff at every update, although I did remove it before. Plus the test results got worse and worse (for example:

      1. Dieu said on November 19, 2014 at 9:25 pm

        I use Avira Free too but I use the Version 12 which is lighter than current version.

        I tweaked a bit Avira and don’t see any ads to upgrade or message, the power of an antivir is it’s databse and mine is updated everyday.

      2. Seban said on November 17, 2014 at 10:04 pm

        Thanks Bob. I’ll have a look at 360 Total Security later, sounds interesting.

      3. Bob Sireno said on November 17, 2014 at 2:25 am

        Seban: You made the right move ditching the current incarnation of Avast. I check with AV-Test and AV-Comparatives monthly to see what their latest tests show. Avira currently is at the top of its game, like it was four years ago. I personally switched to 360 Total Security which lets me add both Avira and BitDefender engines to its own. This “triple filtering” by a single program works very well.

  19. Ron said on November 16, 2014 at 4:44 pm

    Go back to Avast version 9. I did (for other reasons). I sure hope the next major version is better, or I may have to go back to AVG.

  20. Solop said on November 16, 2014 at 4:35 pm

    >:( I’m experimenting exactly the same!

    I was searching around thinking one of the latest Firefox updates removed some of my extensions and, thanks to this blog, I realise it was Avast!!

    I’ll follow your advise and will backup my extensions before Avast removes all of them…

    Thanks for the heads up!

  21. kalmly said on November 16, 2014 at 3:44 pm

    Oh wonderful. The last thing I did before shutting down my Win7 computer was to let AVAST update.

  22. Joe said on November 16, 2014 at 10:07 am

    Same thing happened to me. However, I did use the Browser Cleanup tool right around the time I noticed the extensions missing and I am highly suspicious of Browser Cleanup. In fact, I disabled several of the Avast tools — Browser Cleanup and Grime Fighter, etc. Since doing so, the problem has not recurred.

    I have not tried Mozbackup because I regularly use the FEBE extension, which enabled me to restore my missing extensions right from Firefox. It is also an option for users — and it works on any OS platform:

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