You can check for issues caused by a corrupted or incomplete Visual C++ installation that is missing runtime components (Redistributable Packages) required by Firefox, especially VCRUNTIME140_1.dll.

See "Visual Studio 2015, 2017, 2019, and 2022":

• https://docs.microsoft.com/en-US/cpp/windows/latest-supported-vc-redist
• https://aka.ms/vs/17/release/vc_redist.x64.exe
• https://aka.ms/vs/17/release/vc_redist.x86.exe

You may also have to install the Visual Studio 2013 Redistributable Package. You need to reboot the computer.

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Try it from Mozilla and see what happens. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

You can also check the Windows Event Viewer logs to see if there is more detail available.

Thanks for the help cor-el.

I have installed these programs which I believe are the ones that you asked me to install. Microsoft Visual C++ 2012 Redistributable (x64) Microsoft Visual C++ 2013 Redistributable (x64) Microsoft Visual C++ 2015 - 2022 Redistributable (x64)

I have checked and I do have VCRUNTIME140_1.dll in System32. I have restarted my PC and reinstalled Firefox, but it is still having the same problem.

jonzn4SUSE I have also installed Firefox from that link but I still have the same problem.

What do I need to do?

Try to start Firefox in Troubleshoot Mode to see if that works.

• Windows: hold down the Shift key while starting Firefox
• Mac: hold down the Options key while starting Firefox

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode

Unfortunately that doesn't seem to work. I have noticed that I have had the same problem when trying to open Chrome.

What security software are you running? What version of Win11? If Pro, can you fire up Windows Sandbox and see if you have the same issues in the VM? https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

The security software that I am using is Bitdefender, and it doesn't seem to be the problem. The version of W11 I am using is Windows 11 Home 22H2.

As a test... disable BitD, reboot and try again.

I have found the solution (and I'm upset that I didn't find it earlier.) Microsoft has made a setting for when you belong in a Microsoft Family. It restricts you from using any other browser apart from Edge (which it didn't really work well because Opera worked.) There is another Firefox support thread outlining this: https://support.mozilla.org/en-US/questions/1378744

Thanks to everyone who helped me. I find it really stupid that Microsoft did this.