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://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads *https://aka.ms/vs/16/release/vc_redist.x64.exe *https://aka.ms/vs/16/release/vc_redist.x86.exe You may not need the latter (32-bit version) if you use 64-bit Firefox. You may have to reboot the computer.