If you have downloaded the Firefox setup file (for Firefox 3.6.15 it will be called Firefox Setup 3.6.15.exe), run it by double-clicking on the file to install Firefox.

https://support.mozilla.com/kb/Installing+Firefox+on+Windows

Where would you find the file? I dont even know where to look for it.

You can find the latest Firefox release in all languages and for all Operating Systems here:

• Firefox 12.0.x: http://www.mozilla.org/en-US/firefox/all.html

• Firefox 3.6: http://www.mozilla.org/en-US/firefox/all-older.html

Be aware that Firefox 3.6.x versions are no longer supported with security updates.

• https://support.mozilla.org/kb/firefox-36-no-longer-supported