I understand you recently updated Mozilla Firefox on your computer and then the browser started showing an incompatibility warning with itself. This can happen occasionally after Firefox updates to a new version.

The most likely cause is that the browser did not fully clean out older leftover Firefox files and data when installing the update. So when it launches, Firefox detects these older components and incorrectly thinks an incompatible version is already installed.

The good news is this can usually be easily fixed by fully uninstalling Firefox and doing a fresh clean reinstall of the latest version. Here are the recommended steps:

Completely uninstall Firefox, being sure to check the box to delete all Firefox data and settings. This erases any leftover files. Restart your computer after uninstalling. This clears out any Firefox processes still running. Download the latest Firefox installer from the Mozilla website. Run the installer to reinstall Firefox fresh. No need to delete anything this time. Once installed, Firefox should launch normally without any incompatibility warnings. Doing a full clean reinstall ensures you have only the latest Firefox version without conflicting old data. Let me know if the issue persists after following these steps. I'm happy to provide any other troubleshooting suggestions to get Firefox running smoothly again after the update.

An error message about XPCOM missing or about platform version usually happens because of a failed Firefox update that left you with a mixture of old and updated files in the Firefox program folder. This can happen in case security software was keeping a handle of some of the files in the Firefox program folder preventing Firefox from replacing all the files. You need to do a clean reinstall and remove the Firefox program folder to ensure that all files are replaced. You may have to disable security software temporarily in case the problem persists.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

I've searched for everything that could possibly be hidden in C:, rebooted, hard shutdown, safe start-up, and nothing works. I still cannot download it without the virus scan indicator.

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot

I've searched for everything that could possibly be hidden in C:, rebooted, hard shutdown, safe start-up, and nothing works. I still cannot download it without the virus scan indicator.

What are you using for your antivirus or scanner and what is the message given?