Fixing Firefox's Couldn't load XPCOM error message on start

Martin Brinkmann
Dec 10, 2013
Updated • Apr 14, 2018

When I tried to start the Firefox web browser today I received two error messages instead of the web browser. It would not start because of this, which left me puzzled for some time.

The first error read "The program can't start because pgort100.DLL is missing from your computer. Try reinstalling the program to fix this problem". The only option was to hit on ok, which caused the second error prompt to appear on the screen.

This time it read "Couldn't load XPCOM".

I'm running Firefox Nightly, the cutting edge version of Firefox which sometimes has issues. It happens rarely, and I never ran into startup issues before when using the browser.

How to fix Couldn't load XPCOM

couldnt load xpcom

It was very likely that the last update of the browser somehow caused the issue. Either because it was not applied correctly, or because something had not been updated properly.

Whenever I encounter errors surrounding DLL or other loading errors, I restart the PC to see if they go away afterwards. This time though, a restart did not resolve the issue. The could not load issue was still being displayed on the screen.

I then tried to find out more about the dll that was missing: PGORT100.dll. A quick web search revealed that it was part of Microsoft's Visual Studio, the Microsoft Profile Guided Optimization Instrumentation Runtime.

pgort100.dll is missing

I was not able to locate it on the system. Instead of searching for that file now on the Internet, I made the decision to simply install Firefox anew.

A new installation should add the missing file back to the system, and since it does not touch the profile directory at all -- which contains all the custom data of Firefox like bookmarks, browser extensions or themes -- it should not cause any further issues.

I knew that the issue would not be solved if it was an issue of the latest Nightly build, and not a local issue that only I was experiencing.

Still, it was my best shot. I downloaded the latest Firefox Nightly build and installed it to the same directory that the previous installation was installed in.

I then launched Firefox and lo and behold, the XPCOM error was gone and the browser did start up like usual.

In short, here is what you may want to do:

  1. Restart the PC and try to load Firefox again. If the error persists, go to 2.
  2. Download the latest Firefox installation file from Mozilla and install the web browser over the existing installation to fix the XPCOM error.

Note: As I mentioned earlier, this fixes the issue only if the actual Firefox version that Mozilla pushed out is not buggy. If you run Nightly or Beta, chance is that you will receive versions every now and then that have issues. That's to be expected as yo deal with beta and development software.

Closing Words

If you are experiencing pgort100.dll or XPCOM related error messages in Firefox during start, try installing the browser anew.

I still do not know what caused the issue in first place. In my case, the most likely explanation is that the most recent Nightly update somewhat got things messed up so that some files were not updated correctly.

Fixing Firefox's Couldn't load XPCOM error message on start
Article Name
Fixing Firefox's Couldn't load XPCOM error message on start
Find out how to fix the Firefox error Couldn't load XPCOM quickly that you may receive when you try to start the web browser on your computer.
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  1. Gary said on April 5, 2020 at 9:39 pm

    Windows XPCOM errors. qwindows.dll

    It fixed my XP,.but I dont know about any other Windows. I think It is a repair tool dll.

  2. Augusto Aguas said on March 20, 2020 at 2:40 am

    In my PC, Windos 7, it happen with ALL the browsers, including during the installation. I must believe the glitch is on my computer. I dont know where to find a solution !

  3. wet said on October 28, 2017 at 1:47 am

    so, nobody knows why it happens – ok
    Happened to me today. i don’t update firefox so it can’t be that. Been having problems with this hard drive always wanting to run a checkdisk so it’s probably that in my case, but not sure why it’s happening on other people’s machines.
    The only other thing that coincides with another’s comment about TOR is that i installed a VPN recently and used FF through that.
    Apart from that we still don’t know why this happens.
    I couldn’t open Edge either, so i did a system restore which fixed it.
    I use OpenVPN.

  4. Gary(aged 75) said on August 28, 2017 at 5:56 pm

    I know its an old thread-but feel I must add my comment!.This problem has caught me out twice,once using Windows XP about 18 months ago,and again this week using Windows7 on a fairly new computer. I used the Firefox browser on both computers. I could not go on-line using XP to download a new version of Firefox as even IE would not connect to the Internet on my old XP computer. The repair man said”My computer was too old and outdated”. So he sold me a newer computer with Windows7 loaded…….. It works fine and I downloaded and use Firefox-,until a couple of days ago. Luckily,IE is still working,so I deleted the Firefox program and downloaded the current version. I’m not a computer expert,but I now know that the Firefox program consists of MANY individual files,including the file that allows it to connect to the web.I can only assume that this file got corrupted during the last Firefox update a few days ago. As I still have my old XP hard drive,I might just try a little experiment one day…….. I am indebted to the writer of this article for the simple explanation! Thanks,

  5. Kelly said on January 13, 2016 at 12:05 am

    Can i ask Have you Tor installed on your machine this message frequently comes up when trying to start Tor and what one does is uninstall it run a cleaner and reinstall Tor. But it still does not explain what Xpcom is

  6. Pat Caplis said on December 12, 2015 at 6:52 am

    I uninstalled everything but nothing connects to the internet to download or anything. Never use that app and had this error on my computer this morning. What a pain!!

  7. Brian said on October 20, 2015 at 8:36 pm

    I got the xpcom error today. Problem is if i unistall it, my internet explorer doesnt load either so i can not reinstall it…

  8. Lorissa said on October 1, 2015 at 7:47 pm

    I realize this thread is very old, however the XPCOM problem still exist as of today. Two days ago I updated Firefox to version 41.0. Yesterday my trial period for Kaspersky Internet Security 2015 expired so I decided to try the 2016 version. I won’t bore anyone with the details of how I totally removed the old version and install the new cleanly (I do know what I’m doing). The install went perfectly as did the scans and database download. However, when I attempted to run Firefox the XPCOM message appeared. This not making any sense, I open Chrome and it ran fine. I disabled Kaspersky and load Firefox again. It worked just fine. So, in my humble opinion, this problem had to do with Kaspersky and not Firefox. I install Avast! and everything runs fine.

  9. Ken Saunders said on December 11, 2013 at 12:58 pm

    I’ve occasionally run into startup issues with Nightly (one in the past month), but it’s rare and bugs are usually filed and resolved fairly quickly.

    1. Martin Brinkmann said on December 11, 2013 at 1:00 pm

      I agree. During my research I noticed that the error may also appear if you are using other versions of Firefox. It is not as rare as you may think, at least judging from the number of help threads that cover it.

  10. WandersFar said on December 10, 2013 at 5:20 pm

    I also got this error yesterday, and went through a similar troubleshooting process.

    Unfortunately, Nightly hadn’t been updated when I went to re-install, so I downloaded Aurora instead. I actually think I might just stick with Aurora from now on. It’s less likely to exhibit these issues.

  11. Michalis said on December 10, 2013 at 12:32 pm
  12. Filou said on December 10, 2013 at 10:03 am

    Thanks for the tip ;p

  13. ilev said on December 10, 2013 at 6:55 am

    Firefox 26.0 is out.

    1. abdul raheem said on September 29, 2014 at 2:34 am

      I need to fixing firefox couldn’t load xpcom

    2. Martin Brinkmann said on December 10, 2013 at 8:23 am

      And so is my what’s new guide ;)

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