Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

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 and 2019":

• https://docs.microsoft.com/en-US/cpp/windows/latest-supported-vc-redist
• https://aka.ms/vs/16/release/vc_redist.x64.exe
• https://aka.ms/vs/16/release/vc_redist.x86.exe

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