Inquiry: Intermittent Firefox crashes (xul.dll?)

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Hoang (US), Victor T

May 17, 2021, 6:21:20 PMMay 17

Hello everyone,


I was wondering if anyone has experience with something I’ve been addressing the past month. My organization has been experiencing a large increase (and recurring) issue with Firefox ESR crashing unexpectedly. When it goes down, it is unable to open in safemode, and persists even upon reinstalling. Only way to resolve it, is to restart the (windows 10) PC, and refresh the profile (or creating a new one). Doing so resolves the issue temporarily (1-3 days), but then symptoms come back. I have noticed that deleting the place.sqlite file is another alternative, but still has the same problem several days down the road. It’s the same people repeatedly that have the problem so I’ve been monitoring the websites/applications they use as potential culprits.


The trend I’ve noticed with over 30 customers I’ve contacted is that in the Windows 10 Event Viewer, the error logs for Firefox says the “faulting module” is xul.dll. Googling I’ve seen vastly different solutions ranging from disabling antivirus, to faulty memory, to using about:support and refreshing the profile or reinstalling firefox.


Heres an example of the Event Viewer text (its mostly the same from person to person)…if anyone has experienced the same thing I’d appreciate any information! All of my solutions have only been temporary…(refreshing profile, reinstalling browser, Sanitize Cache in policy.json, deleting the places.sqlite file in the user profile, and ensuring only 1 version of the browser is installed).



Faulting application name: firefox.exe, version:, time stamp: 0x60900fbe

Faulting module name: xul.dll, version:, time stamp: 0x60900fe4

Exception code: 0xc0000005

Fault offset: 0x000000000038c2ec

Faulting process id: 0x4d04

Faulting application start time: 0x01d746beb778852a

Faulting application path: C:\Program Files\Mozilla Firefox\firefox.exe

Faulting module path: C:\Program Files\Mozilla Firefox\xul.dll

Report Id: cf48af8c-644a-40bc-ac42-2cc998235f63

Faulting package full name:

Faulting package-relative application ID:


- <Event xmlns="">

- <System>

  <Provider Name="Application Error" />

  <EventID Qualifiers="0">1000</EventID>




  <TimeCreated SystemTime="2021-05-11T23:38:18.864162900Z" />




  <Security />


- <EventData>











  <Data>C:\Program Files\Mozilla Firefox\firefox.exe</Data>

  <Data>C:\Program Files\Mozilla Firefox\xul.dll</Data>


  <Data />

  <Data />






Mike Kaply

May 17, 2021, 7:18:26 PMMay 17
to Hoang (US), Victor T,
Do these crashes get reported to Mozilla?

Do you see them in about:crashes


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Hoang (US), Victor T

May 21, 2021, 1:30:04 PMMay 21
to Mike Kaply,

Sorry for the delay in response, I needed time to collaborate with some colleagues.


I disabled crash reports initially due to information security concern. I got permission for a small subset of users to temporarily enable it.


Normally when my end users have this crash, I was unable to grab the crash report because I’d need to completely uninstall and blow away their profile to get Firefox back up and running. Luckily, one user was able to get back on and reach about:crashes to send some reports that were generated.


Here are the links to those reports:


Let me know if you need anything else (I’ll be looking at these as well),



From: <> On Behalf Of Mike Kaply
Sent: Monday, May 17, 2021 4:18 PM
To: Hoang (US), Victor T <>
Cc: <>
Subject: [EXTERNAL] Re: [Mozilla Enterprise] Inquiry: Intermittent Firefox crashes (xul.dll?)


EXT email: be mindful of links/attachments.


Hoang (US), Victor T

May 25, 2021, 1:21:14 PMMay 25
to Mike Kaply,
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