Another Windows 7 user is having trouble with Firefox 49 not updating or installing correctly. See: Missing mozglue.dll when launching Firefox - temporarily solved by installing Firefox 48.0.2, but it tried to update again right away.

The issue with the Mozilla Maintenance Service is interesting, but I don't think that would affect the full installer. ??

When I search around for that error code/message, the causes seem to be extremely diverse. Perhaps something that Firefox 49 assumes is normal on Windows is just a bit different on some systems. Tracking down what it is looks to be a challenge.

For example:

• https://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/The-application-was-unable-to-start-correctly-0xc0000142.html
• http://deshack.net/windows-how-to-solve-application-error-0xc0000142-and-0xc0000005/
• http://answers.microsoft.com/en-us/msoffice/forum/msoffice_word-mso_windows8/the-application-was-unable-to-start-correctly/b28dd2ae-3bde-4102-9081-eff1c50581e4

Hi Linda, What security related software are you using ?

Other reports of this may have been due to security software quarantining or sandboxing Mozglue. Are you able to find the mozglue.dll in the Firerfox program folder ?

Hi jscher 2000

The mozglue.dll file is present, so I don't think your advice to another Windows 7 user applies to me.

Hi John99

I'm using Security Essentials and Windows Firewall. If I shut them off Firefox still does not launch. Do I need to download Firefox again with them shut off?

I also use Malwarebytes but it's the free one, which only runs when I ask it to do so.

I think for now we can ignore mozglue, because you do have the file present. As Jscher200 remarked the cause of this particular error appear diverse. Some have reported that the Windows File Checker should be run to address this issue. Perhaps that will help in your case. This MS article explains how to run SFC.exe

• Use the System File Checker tool to repair missing or corrupted system files
  https://support.microsoft.com/en-us/kb/929833

If it is a Firefox issue a clean reinstall may help. That entails deleting all the Firefox program files before reinstalling Firefox. It is not something that always helps. It may be needed if Malware or Security software has been messing with Firefox files. Note NOT to delete Firefox profile files (profile issues can be dealt with separately if necessary).

Often we are fairly certain of the cause and solution, in this case I'm resorting to guessing.

Clean Install

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles. Thank you.

Hello John99,

I ran SFC tool as you instructed. Which was quite a lot easier than I feared. Thanks for the hand leading.

Result: " Windows Resource Protection did not find any integrity violations."

Re: Revo uninstaller warning. Too late. I already ran it a couple days ago. Not to worry about personal files, I backed everything up on an external hard drive about six weeks ago.

I'll try Clean Install next.

When you get Firefox working again you will need to look at this

• Recover important data from an old profile

We seem to be getting more question threads than usual about Firefox 49 not installing or not starting. Others are not reporting your specific error message. Try the clean install but if that fails to help & you want to get an alternative additional Firefox browser up and running for now have a go with the third party Firefox Portable ESR, it will install on a memory stick or on the hard disk drive. (Not an official recommendation. That version is intended for corporate use but it can be handy in emergencies, and ESR does get critical security updates despite it currently being Fx45.4.n )

• http://portableapps.com/apps/internet/firefox-portable-esr

I performed a Clean Install. No joy. Still could not launch Firefox. But, here's a new wrinkle. I wanted to try a launch with Windows Firewall and Security Essentials turned off. I turned off the firewall. I couldn't see how to turn off SE so I clicked on Help, and I got that same, familiar window and error code telling me the application could not start .

Is there any significance? Do you think I should contact Microsoft? Could the Security Essentials program be corrupted somehow?

Have you tried Firefox portable ESR ? & if so and it works have you tried it from a memory stick or the hard drive.

Yes it would be worth contacting Microsoft. It is a Microsoft Error code and apparently now affecting more than just Firefox. Obviously you need SE working properly.

I have not yet tried Firefox portable ESR. Should I try that first or try to ascertain that SE is working properly? I hate to muddy the waters by involving Microsoft, but it's beginning to look like its a MS problem.

This problem is escalating. I'm getting that error code when I try to open downloaded files, help, all kinds of things.

I replaced Security Essentials program, updated, scanned. The problem is worse.

I don't know how long Explorer is going to keep working. If I suddenly disappear from this forum it may mean I have pitched this machine out the window and gone out to buy a Mac.

I'm going to try to get some help from Microsoft (while still hanging onto my wallet).

It may be worth thinking of doing malware scans with all the tools listed in

• Troubleshoot Firefox issues caused by malware

Outside of the scope of this forum so jist a quick comment. Linux comes in many free lightweight distros some will run from memory sticks it could give you a working computer of sorts, and even help with the problems of fixing the faulty Windows &/or accessing your files.

• https://en.wikipedia.org/wiki/Linux_distribution#Installation-free_distributions_.28live_CD.2FUSB.29

Thanks John.

I'll run all the malware programs I haven't already tried and hope for the best.

Update: This may be totally unrelated, or possibly some security software could be involved. One of the people with a mozglue issue is finding His AVG AV security software is causing a problem. Firefox will run when reinstalled but fails to start if the AVG is re-enabled.

Hello John99,

I've scanned with several malware programs and deleted some files they found questionable. I'm now able to open files that previously gave me the error code. I can download and install Firefox without incident now, but it still will not initiate, and I'm forced to use Internet Explorer. IE is still working but it hangs and closes abruptly sometimes, and will not open some things that were downloaded using Firefox. I find it curious that I've not had any problems installing and running malware programs. Whatever is going on here seems to primarily affect Firefox. Is anyone else having this problem?

thanks, from other users we heard that this might be an issue with older version of avg security software - if this applies to you as well, please try to update to a current version (since avg might not maintain older versions of their program anymore): https://support.avg.com/SupportArticleView?l=en_US&urlName=How-to-upgrade-AVG-8-5-9-0-2011-or-2012-to-the-latest-version

I'm not using avg software. I use Security Essentials, Malwarebytes. and a firewall. All are current and up to date, and the firewall is set to allow Firefox to run.

I found an old firefox file in my downloads folder from June and I installed it. It's Firefox 43.0.1.5828. It works fine. Everything was back to normal, but when it updated to version 49 it stopped working.

Does this give anyone a clue about what's going on?

Hi LindaK71, please check if there are any updates for AVG, there was a compatibility issue with a start up crash that was caused in Firefox 49, I believe an update went out.