Hi, look in your AV program to make sure that Firefox isn't being blocked. Also if you have any AV software, such as that which may install a toolbar on Firefox, try disabling to test.

Try 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.

Please report back to say if this helped you!

Thank you.

Hi Scribe, I tried this already 2 days ago and again just now. After installing latest Firefox version 49, when I launch it, I get error about missing mozglue.dll in C:\Program Files\Mozilla Firefox\. That's why I raised other support issue https://support.mozilla.org/en-US/questions/1140005

If I uninstall version 49 and install version 48.0.2, it installs mozglue.dll and Firefox 48.0.2 can be launched, however it automatically updates with the latest version 49 and upon closing Firefox and relaunching it, I get the error mentioned in this support issue (i.e. "The application was unable to start correctly (0xc0000022). Click OK to close the application". ).

Note that I have disabled my Antivirus during these tests and that did not help.

Is there anything else I can try?

Regards

Hi again, this is proving to be a hard nut to crack, so I've escalated your question, in order that Mozilla's top techs can investigate further. They're currently looking into it and will get back to you with more details ASAP. Please understand that escalations can take up to 72 hours for a response, but might be a bit longer as it's a weekend.

Hi andrewli7, is this issue resolved now in light of your post

• Missing mozglue.dll when launching Firefox /questions/1140005#answer-922975

Hi philipp, I removed AVG 2014 and installed AVG 2016 and it fixed the problem. I can now use Firefox with AVG enabled. Thanks.