How to Manually Update Firefox with MAR File on Windows

Whenever Mozilla releases a fresh new update for the Firefox web browser, it is made available on their FTP server many hours before you actually receive the update through automatic updates. If you cannot wait, then you can either download the full installer for the new version and install it on your system, or you can download a smaller partial update MAR (Mozilla Archive) file and manually update your Firefox browser.

Here is how you can manually update Firefox on Windows using the partial update MAR file:

  1. Create a folder where all our update files will be kept. For example, I have created D:\Update.
  2. Visit and find the latest version of Firefox. Inside that version directory, you will find an update folder where you can find the MAR files in various sub-folders. The MAR files are named to tell you which old version can be updated to which new version. For example, firefox-89.0.2-90.0.2.partial.mar can update version 89.0.2 to version 90.0.2. Choosing a wrong architecture or MAR file will result in update failure. Manually Update Firefox Using MAR
  3. Right-click on the Firefox shortcut on your Windows desktop and select Open file location. This will open the installation folder where Firefox is installed. Typically, it is C:\Program Files\Mozilla Firefox.Manually Update Firefox Using MAR
  4. Copy updater.exe and updater.ini from Firefox installation folder and paste them in the update folder D:\Update. Copying of the updater.ini is optional, it is just for showing a update progress.Manually Update Firefox Using MAR
  5. Copy the downloaded MAR file (step 2 above) in the same folder (D:\Update) and rename it to update.mar.Manually Update Firefox Using MAR
  6. Open an elevated command prompt (press Win+X and then select Command Prompt (Admin)) and then give the following command:
    D:\Update\updater.exe D:\Update "C:\Program Files\Mozilla Firefox\" "C:\Program Files\Mozilla Firefox\"

    Manually Update Firefox Using MAR

  7. In the update folder (D:\Update) check the update.log file. If it has succeeded near the very end, then update process has been a success. Without seeing “succeeded”, do not follow the next steps. If it is not success, then you should check the command line and the MAR file.Manually Update Firefox Using MAR
  8. Copy the update.log from D:\Update inside the uninstall sub-folder of the Firefox installation directory. In our case, we copied it to C:\Program Files\Mozilla Firefox\uninstall.
  9. In the elevated command prompt, give the following command:
    C:\Program Files\Mozilla Firefox\uninstall\helper.exe /PostUpdate

    Manually Update Firefox Using MAR

Now you have successfully updated Firefox to the new version using the small partial MAR update file. This is a complicated process, but now you know yet another way to update Mozilla Firefox browser on Windows.