Firefox 100 on Windows 7 requires update KB4474419

Starting with Firefox 100, Windows 7 SP1 users must have the KB4474419 update installed before installation of the Firefox browser, otherwise it may not work. This is because Mozilla has signed the Firefox installer for Windows with a SHA-256 digest than SHA-1. Below, you can check and verify that you have the mandatory security update installed, if not, we have covered the instructions on how to manually install the KB4474419 update.

Firefox 100

Some Windows updates, especially security updates, are quite mandatory. If users don’t install them on their devices, Windows might not work properly and you won’t be able to install certain apps either. This is the case for Firefox 100 version on legacy Windows OS.

In 2019, Microsoft dropped SHA-1 and introduced SHA2 code signing support for Windows 7 SP1 and Windows Server 2008 R2 SP1 and Windows Server 2008 SP2 with KB4474419.

You may have the update automatically installed in October 2019, here’s how to check.

  1. Open Control panel
  2. click in Software > Programs and features >
  3. Click in “View installed updates
  4. Search for KB4467719 if you “Security Update for Microsoft Windows (KB4474419)” listed, you don’t have to worry. After updating or installing Firefox 100, it will run smoothly.
    KB4474419 update not listed in installed updates for Windows 7

If you don’t have the required update installed, you may not be able to install Firefox. For example, in the past, Kaspersky threw this error for not having the update.

“The operating system does not support SHA-2 as a signature algorithm. To install the application, you must install Windows Security Update KB4474419”.

Firefox installer for Windows comes signed with SHA2-digest

“As of this release, the Firefox installer for Windows is signed with a SHA-256 digest instead of SHA-1. Update KB4474419 is required for successful installation on a computer running the Microsoft Windows 7 operating system,” noted Mozilla.

You can install this update on Windows 7 SP1 through Windows Update or the Micorsoft Update Catalog.

How to install KB4474419 update manually

  1. visit Microsoft Update Catalog and look for update KB4474419 for Windows 7
  2. Select x86 or x64 OS version and click the button download button
  3. double click on .msu file, and the update will be downloaded. Run it once the download is complete to start the installation.
  4. After installing the update, restart your computer.

How to install Firefox 100 on Windows 7

1. After installing the KB4474419 update, visit This page

2. And download Firefox browser and install it on Windows 7.

Firefox does not support Windows Vista anyway.

This change does not affect Firefox running on Windows 8, Windows 10 and Windows 11.

Firefox 100 is scheduled to be released on May 3rd.

With the user agent string reaching a three digit number, some websites may not work in this version

As of writing the article, we were able to successfully install the beta and nightly versions of the affected version of Firefox on Windows 7 that does not have Update installed without any issues.

Are you still using Firefox on Windows 7? Why didn’t you upgrade to Windows 10 or Windows 11? Let us know in the comments below.

More about Firefox:

Firefox 98 Coming Today: Here’s What’s New, Changed, and Fixed

Firefox Picture-in-Picture gets YouTube subtitles and subtitles support

How to Restore Download Prompt in Firefox 98

Mozilla Firefox gets Windows 11-style scrollbars

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