Firefox 85.0.2 is out with a single deadlock fix

Martin Brinkmann
Feb 9, 2021

Mozilla has released Firefox 85.0.2, a stable channel update for the organization's Firefox web browser. Released for all supported desktop operating systems, Firefox 85.0.2 fixes an issue that is exclusive to certain devices running Apple's Macintosh operating system.

The official release notes are published already, stating that the new version of Firefox "fixes a deadlock during startup". The linked bug report on Bugzilla@Mozilla provides additional details about the issue.

The issue was reported two months ago. The reporter stated that the issue affected Mac OS Big Sur and Mac OS Caralina devices running Firefox., and that Firefox would hang when trying to launch a new window from the context menu using the icon on the Dock.

Steps to reproduce
Launch Firefox.
Try to open a new window from the context menu on the icon in Dock
Actual Result
Firefox is not responsible with rainbow cursor.
Firefox does not comeback and I need to quit Firefox forcely.
I reproduce this bug a few days ago.
I does not face this bug rarely on a new profile

The issue affected Firefox Nightly at the time but it seems to have been included in the beta and stable releases of Firefox 85 as well. Mozilla's update to Firefox 85.0.2 resolves the issue.

Firefox users may select Menu > Help > About Firefox to check the installed version and run a manual check for updates. Users whose version of Firefox is unresponsive may download the new release from Mozilla's official download site to install it manually after the download completes.

It looks as if the fix will also land in Firefox ESR, but it has not been released yet it appears. Mac users who run the ESR version of Firefox and experience the issue may monitor this link for changes.

Mozilla released Firefox 85.0.1 just three days ago to fix a critical security vulnerability in the browser. The next major release is Firefox 86 Stable; it is scheduled to be released on February 26, 2021.

Firefox 85.0.2 is out with a single deadlock fix
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Firefox 85.0.2 is out with a single deadlock fix
Mozilla has released Firefox 85.0.2, a stable channel update for the organization's Firefox web browser. It fixes a deadlock on Mac OS X devices.
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  1. Egain said on February 23, 2021 at 9:06 am

    After 85.0.2 my firefox become terrible instable (a fresh win10 installation with 3-4 progs).
    Crashes of pages on videos and just after loading the gmail(!) ang gmaps (randomly). In simple case only the page collapses other time the whole program.

    Déjá vu! Similar happens time by time with firefox this. Obviously this program deserves better.

    Maybe they should fire finally the obviously incompetent CEO. Then she would have enough time to think about “whole internet and more …” and the company could find finally someone who able to think about their products and tasks.

    Nothing personal just the sad reality…

  2. ben said on February 16, 2021 at 11:28 pm

    since updating to this version, “print” function causes a 20 – 30 second delay in any functionality.

  3. Haakon said on February 10, 2021 at 7:28 pm

    Oops. I forgot to mention that link to id=167933 I posted is the one in the “provides” link in Martin’s second paragraph above.

  4. Haakon said on February 10, 2021 at 7:09 pm
    Comment 22 (bullets mine):

    “I think the code that triggers this deadlock was in bug 1325341 (since the lock is mRCWNLock), so it has been there for years. I think it’s probably some •recent changes that affect the thread timings and make this deadlock happen more often• Unfortunately, I can’t tell how many users are affected, since it’s all about timing to hit this.”

    I can’t recall when my PortableApps Firefox has ever failed to start up going on 15+ years (Thanks, John!).

    As well, it’s seems the only way to reproduce this demonstrably and consistently is on a Mac.

    I’ll stick with 85.0.1 on my Win10 systems. Next update: 86.0.1.

  5. off topic said on February 10, 2021 at 12:42 pm
    1. ShintoPlasm said on February 10, 2021 at 2:30 pm

      I swear it looks more and more like Chrome every day.

  6. Anonymous said on February 10, 2021 at 7:34 am

    This deadlock bug also affects Windows and Linux as well, it’s not just Mac. You might want to spend some time reading the actual bug report (or even just the “references” section, located in the header of the thread), which references multiple of these other related/duplicate bugs that affect the other platforms, e.g.:

    1689032 – Firefox 85.0 freezes on Windows, macOS 10.15.7 & linux on startup:

    1690347 – Firefox 85 on Win10 freezes on startup:

    1684966 – Deadlock during Browser Toolbox startup in nsHttpChannel::SetupTransaction -> nsHttpChannel::OnCacheEntryCheck -> EnsureNSSInitializedChromeOrContent() -> sync main thread runnable:

    I for one, am on Win 10, and have spent I’d say the past week or so, vigorously trying to figure out what the problem was with my startup and trying (unsucessfully) to fix it. Hope this finally does fix it. Was driving me nuts.

  7. Anonymous said on February 10, 2021 at 6:43 am

    If this is for only Mac,then I got it for Windows like the other anon said. So they just pushed this out for everyone. For those who don’t like Mozilla or Firefox,there is a privacy focused fork called

  8. Tim said on February 9, 2021 at 11:34 pm

    Why do I get the sense that the author of this article has no idea what the word deadlock means even though he put it in the title of his article?

    1. Haakon said on February 10, 2021 at 7:18 pm

      He knows exactly what it means, as do most of those who visit this site. Some of us since about 2007 or so; I forget exactly when.

      And those who have sense would use a good search engine to find out what it means relative to this context here before posting up they have no sense.

  9. Ikhan said on February 9, 2021 at 8:06 pm

    This problem don’t have Linux

  10. Anonymous said on February 9, 2021 at 7:22 pm

    Since I’m running Windows 10, why does Firefox give me a notification to update to 85.0.2 which is to fix a problem on Mac?

    Suggestion to Mozilla: Only push out updates if they are appropriate for that platform.

    It is amazing how much time I spend updating my system, and doing the needed the research to make sure the updates don’t break anything.

    There has to be a better way.

    1. Anonymous said on February 10, 2021 at 7:51 am

      To maintain there numbering system 85.0.1, 85.01.02 etc

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