If you have all ready save the download file, double click on it and the Mozilla Firefox Setup Wizard will open.

see for more info : Installing Firefox on Windows - Starting the installation

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files by Firefox and installing Firefox.
Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.

See:

• http://kb.mozillazine.org/Unable_to_save_or_download_files

Where is your internet download folder? Downloading (if successful) is the first step once you selected SAVE.

You might have saved a step by selecting RUN instead.

If the setup file is on your computer (what browser did you use?) it will be in the directory/folder that your browser uses --- you can find out easily.

Once you find that downloaded file, execute that file by whatever sequence you have selected for your mouse clicks to open.

I know this sound terribly basic, but sometimes it's the simple things that are forgotten or that others don't think are pertinent.

Cheers ----