I will see to it... Thanks

Hello,

You may have seen a post or received a notification regarding support for Firefox or Thunderbird with a link to another site or a phone number being posted. This is a scam and is not a method to receive support from Mozilla. Mozilla does not have telephone or email support. Please do not click on the link and do not interact by calling any phone numbers or email addresses listed. I apologize for any inconvenience caused. You are currently posting on the official Mozilla website and will receive assistance here.

Thanks for the info.

I don't know why you are getting an XULRunner: Couldn't read application.ini error when first starting your computer. Whichever program is causing the error is set to run at Windows startup.

Assuming this is related to Firefox, the file application.ini is located inside the C:/Program Files/Mozilla Firefox folder on my Windows (64-bit) computer. Are you unable to start and run Firefox? Your system details show User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.97 Safari/537.36 meaning you did not use Firefox to post this thread.

Firefox won't start - find solutions has an "XULRunner - Error" section that suggests a clean reinstall of Firefox (uninstall Firefox, delete leftover program files, then reinstall Firefox from a fresh download), but it's not your specific error message.

If you don't get a better answer, you could try uninstalling Firefox from your computer and then do a clean reinstall of Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

More information about reinstalling Firefox can be found in here,
Troubleshoot and diagnose Firefox problems under 4: Reinstall Firefox

Hello,

There is no problem with the browser currently but I get this error message each time I switch on my PC.

The application.ini file is also part of other Mozilla programs, such as Thunderbird. Do you have any problems running any other Mozilla programs?

If your only issue is the XULRunner error reading application.ini when your first start Windows, try to find out which program is causing the issue by disabling any unneeded programs from starting automatically. See these articles for help with that:

https://support.microsoft.com/en-us/help/4026268/windows-10-change-startup-apps

https://www.tenforums.com/tutorials/2944-add-delete-enable-disable-startup-items-windows-10-a.html

If you need more help you could ask in a forum such as https://answers.microsoft.com/windows/forum or https://www.tenforums.com since Mozilla Support is for help with problems using Firefox and Thunderbird.

Hello,

Thankfully it has stopped now and the problem was that an older version of Firefox was not completely uninstalled from the system due to which I used to get the message. After cleanly and completely uninstalling it this message never showed up again.

Thanks for your active responses.

Thanks for posting back that completely uninstalling an older version of Firefox solved the problem.