Beginning with Firefox version 100, Microsoft security update KB4474419 is required for successful installation of Firefox on a computer running the Windows 7 operating system. For details about this Windows update, visit the Microsoft Technical Support website.
Most Windows 7 users will have Microsoft update KB4474419 already installed, since it was an automatic Windows update. To make sure this update is installed on your computer:
- Click the Windows Start button or press the Windows key .
- In the Start Menu, click .
- In the Control Panel window, click the Programs link, then click Programs and Features.
- Click on and wait for the list to be filled in.
- Search for KB4474419 using the search field in the upper right corner.
If Security Update for Microsoft Windows (KB4474419) is listed, you can install Firefox without any issues.