Update to Windows 11 Breaks Mozilla Firefox

Since Microsoft in their infinite wisdom insists on push the masses into their “flagship” Windows 11 by no longer offering Windows 10 licenses from their site (although still possible to purchase elsewhere), where Windows 10 is supported until 2025, I started to test Windows 10 latest to Windows 11 latest upgrades. The goal is to see if anything breaks, before rolling this update out.

It didn’t take very long after the upgrade to discover two things. One, the Windows updates were stuck in Windows 10 and was unable to update Windows 11 any further. This is a topic for another article. The other, Mozilla Firefox latest failed to execute with the VCRUNTIME140_1.dll not found error. I uninstalled and reinstalled Mozilla Firefox and this did not resolve the problem.


lease download and install the VC Redistributables. VCRUNTIME140_1.dll is included in the 64-bit redist.

MS Visual C++ Redistributable for Visual Studio 2015-19, or 2022

x64 (64-bit): vc_redist.x64.exe


That should help. If it doesn’t, download the x86 version as well.

x86 (32-bit): vc_redist.x86.exe


In this case running only the x64 redistributable was all that was needed to get Firefox operational again. The real question is … why?


  • https://answers.microsoft.com/en-us/windows/forum/all/after-an-update-in-windows-11-i-cannot-open/9185756d-9a77-4846-808b-96d4699fdccb