Mozilla rushes to address an Avast bug that causes crashes in Firefox

Martin Brinkmann
Oct 8, 2022

Thousands of Firefox users reported crashes of the Firefox web browser to Mozilla, the maker of the browser. The, often angry user comments, all reported that Firefox had crashed out of a sudden on Windows machines.

firefox 105.0.3 avast crashes

Mozilla started its investigation and discovered, rather quickly, that Avast software was the culprit. Avast, maker of security products, is a popular choice when it comes to third-party antivirus protections on Windows.

It became clear quickly that the issue affected all versions of Microsoft's Windows operating system on which certain versions of the Avast Antivirus software were installed on. The issue in Avast software was critical, as it was the causing the top 5 desktop browser crashes on Windows on release, and the top 20 desktop browser crashes on release.

Antivirus applications are notorious for interfering with legitimate applications on Windows machines. In this particular case, it appears that Avast versions 18.0.1473.0 and older are causing the crashes of the Firefox web browser.

Mozilla decided to block Avast's DLL files using Firefox's DLL blocklist file to stop the crashes from happening. An update to Firefox 105.0.3 is available already, which includes the new entry to the blocklist.

The new version of Firefox Stable addresses just the one issue. According to it, the crashes may also be caused by AVG Antivirus software. Avast acquired AVG in 2016 and has since then brought antivirus products closer together.

Mitigated frequent crashes for Windows users with Avast or AVG Antivirus software installed

Firefox users who run Avast or AVG software may want to update the Firefox web browser to the latest stable release right away. They may also want to check for Avast or AVG updates as well to make sure the latest versions of the security applications are run on the system.

Mozilla employee Gabriele Svelto has another suggestion: uninstall Avast or AVG products.

Firefox users may select Menu > Help > About Firefox to update. If the browser does not open, they may download Firefox from the Mozilla website instead to install the update.

Closing Words

Bugs or false positives are common, and they may lead to crashes of third-party applications and other issues. Often, users of these programs blame the innocent third-party application and not the real culprit, the antivirus solution, when crashes or other issues occur.

Issues like these may see numerous users migrate to another browser, with a good chance that they are lost for the foreseeable future.

Mozilla reacted very quickly to the issue, which is commendable.

Now You: when was the last time you experienced crashes in programs that you use?

Mozilla rushes to address an Avast bug that causes crashes in Firefox
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Mozilla rushes to address an Avast bug that causes crashes in Firefox
Mozilla launched Firefox 105.0.3 to address a serious crash issue caused by bugs in Avast and AVG security products for Windows.
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  1. Mystique said on October 13, 2022 at 10:46 am

    Changing to another browser is not so simple nor is it the right thing to do. Avast should be held accountable for their own garbage as this is clearly not Mozilla’s fault.

    Avast has been a bug on computers for as long as I can remember. I recall their stupid puffy winamp like interface when they first appeared. The very fact they have joined forces with another known scumbag of the PC world is really no surprise.

    In regards to commercial AV’s I believe that NOD32 is a reasonably good choice, it does not weigh down your system and runs quietly in your system but at the end of the day be careful what you do online and do not assume that you are safe just because you have an AV.

  2. Dragos said on October 11, 2022 at 8:04 am

    Remember when AV programs goal and task was to protect your computer from viruses? That’s not high on any of their lists nowadays. Even if you pay top dolla for AV, you are getting a bloated turd that harasses you 24/7 and the focus on malware protection is almost nonexistent. Just stick with the crap Microsoft comes with, or move to linux. Don’t touch any free/commercial AV in this day and age, it’s all snake oil.

  3. Ashray said on October 9, 2022 at 4:36 pm

    Just use Brave. There’s always something wrong with FF.

  4. Erthan said on October 9, 2022 at 4:49 am

    The issue on ff 105.0.3 continue with Win7sp1 32bits with avast Home 21.4

    1. Anonymous said on October 9, 2022 at 8:12 am

      Only very old versions are affected, just update to the latest

  5. Anonymous said on October 8, 2022 at 10:57 pm

    Avast seemed good to me like 15 years ago or so. But then it became junkware. And now I use Linux without antivirus.

  6. Evin Rude said on October 8, 2022 at 8:15 pm

    Avast is Satan.

  7. Agnatron said on October 8, 2022 at 3:35 pm

    Fixed install edge

    1. Frankel said on October 9, 2022 at 12:42 pm

      No. Don’t use snakeoil crap AVs and stick with Defender or Linux.

  8. Herman Cost said on October 8, 2022 at 3:33 pm

    Good to see that people here are not blaming Mozilla when Avast is the obvious cause of the problem (of course it is still early :-)). I also agree with the commenters who are wondering why anyone would actually use Avast in the first place.

  9. Paul(us) said on October 8, 2022 at 3:11 pm

    The question “when was the last time you experienced crashes in programs that you use?”

    The last time was before I moved away from discutable quality software like Avast.
    Quit some time ago.

  10. Techno said on October 8, 2022 at 10:10 am

    I think Avast was the one I tried a few years ago that blocked a Windows update. It would get to 99 per cent complete then just hang forever. I removed the AV and the computer updated OK.

    That put me off using any additional AV beyond Windows Defender.

    1. Jek Porkins said on October 8, 2022 at 2:25 pm

      Avira Free is better, probably one of the best in terms of detecting things that are really a threat and not too many false positives. I’ve been using it for 1-2 years now and it’s doing a fine job.

      1. Sol Shine said on October 8, 2022 at 4:06 pm

        @Jek Porkins
        Avira had a good reputation in the past.
        But since 2021 it is owned by NortonLifeLock (formerly known as Symantec).
        Symantec merged with Avast in 2021.
        Both Symantec and Avast had bad reputations, and now they own Avira.
        So I expect Avira to get infected with the bad behavior attitude that Symantec and Avira has.

        Do not foget that a antivirus program runs with admin rights on your computer, and so can track you and collect your private data, more than Google can.

  11. Mystique said on October 8, 2022 at 8:47 am

    A VAST improvement would be completely removing AVAST.

    1. Ashray said on October 9, 2022 at 4:49 pm

      Be brave, use Brave.

    2. Sol Shine said on October 8, 2022 at 3:54 pm


      Nice word play there.

  12. John said on October 8, 2022 at 7:59 am

    I’m not quite sure who the target audience is for AVAST/AVG products these days. People who like to try to guard against additional adware and nagware by installing one adware and nagware program to rule them all and eliminate it’s competition? People who don’t know Windows Defender is a thing? People using no longer supported versions of Windows where Windows really isn’t a thing (or isn’t a full antivirus)?

    Don’t get me wrong, I understand where having a third party antivirus could be beneficial to someone- perhaps catching things the first party one doesn’t, or taking an alternate approach to protecting you that you think is better or has the potential to be. I just don’t see where it would be worth it if the included one actually is to some extent what you are scanning to eliminate (Although, granted, you do at least know AVAST really is just nagging you with ads and isn’t going to steal your ID or randsome your data.) while the free included one is unobtrusive and contains no ads or nags.

    I feel like the niche for AVAST type products kind of disappeared when Windows Defender became a full fledged free antivirus. WD became kind of what you use if you don’t want to or can’t afford to pay for products like Norton and McAfee, and if you want to pay for something better, you pay for something better. There aren’t the legions of people who have no virus protection and want or need a free solution anymore to the point where they are willing to put up with AVAST type annoyances, and it was that old status quo that AVAST and AVG built their business on (They are currently owned by the same company).

    1. Stella Mcintyre said on October 20, 2022 at 4:19 am

      Not quite sure what niche what by far is the most popular antivirus after Defender have is a joke, no?
      “Microsoft isn’t going to protect you against anything” is why there’s incentive on Defender’s constant improving.

    2. borish said on October 11, 2022 at 1:05 am

      I waited too long to purge avast from my system. uninstalled it after saw I saw it making connections to their telemetry servers even after I opted out. Windows runs faster without that garbage. Just get Sandboxie and run web browser, steam or whatever else you can in that. Windows Defender should be good enough for most folks if you’re on Windows 10+ even if microsoft pulls the same tricks. your data is a drop in the bucket with microsoft compared to the data of avasts shrinking user base.

    3. Emanon said on October 8, 2022 at 10:07 am

      Microsoft Defender is not going to protect you against anything, and is the first target to 99% of the malware nowadays, since it’s included in Windows by default.

      Not to mention the huge performance implications in comparison to third-party offers, Microsoft Defender is extremely slow.

      1. John G said on October 8, 2022 at 7:00 pm

        Just use Configure Defender 3.111, and you will get all the available potrection.

      2. Anonymous said on October 8, 2022 at 12:49 pm

        Depends on the user and the type of PC configuration.
        A user with a SSD system doing casual browsing, work, gaming and not downloading pirated apps would remain protected and won’t notice any performance impact while using Microsoft Defender.
        On older systems with HDD it’s pretty bad.

      3. Anonymous said on October 10, 2022 at 10:49 am

        What did you mean? There’s no difference between HDD and SSD in security?

      4. John G. said on October 8, 2022 at 5:00 pm

        Windows Defender can be extremely configurable with Config Defender.
        Just set it at high level and just see the difference.
        Thanks for the article.

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