hello desarico, you're currently using firefox 25.0.1 - you can check that by going to firefox > help > troubleshooting information. i think those system requirements for calling for firefox 23 are outdated & they might have well meant to use firefox 23 or above. downgrading to old versions is discouraged, since that will introduce known critical security vulnerabilities to your system which have been fixed in later versions of the browser: https://www.mozilla.org/security/known-vulnerabilities/firefox.html