Since you’ve already downloaded the file

1. Locate the Installer

Since you used a browser to download it, the file is likely sitting in your Downloads folder.

Go to your Downloads folder

Look for a file named Firefox Installer.exe

2. Run the Installation

Double-click the file and follow the wizard

Make sure you download Firefox from the official Mozilla website and not via a pop-up on some website as that likely will infect you with malware.

See also:

• https://support.mozilla.org/en-US/kb/i-found-fake-firefox-update
• https://support.mozilla.org/en-US/kb/avoid-and-report-mozilla-tech-support-scams

You can find the full installer of the current Firefox release (150.0.1) in all languages and all operating systems here:

• https://www.mozilla.org/firefox/all/desktop-release/
• https://www.mozilla.org/firefox/150.0.1/releasenotes/