Please update to the current Firefox 22.0 release.

• Help > About Firefox

• https://support.mozilla.org/kb/update-firefox-latest-version.
• https://support.mozilla.org/kb/Updating+Firefox

The Firefox 18 version that you currently run is no longer supported with security updates.

• It is important to update Firefox and add-ons to the latest version to get all security fixes.

You can consider to install the latest Firefox 17 ESR version to access that website.

• http://www.mozilla.org/en-US/firefox/organizations/all.html

• http://www.mozilla.org/en-US/firefox/17.0.7/releasenotes/

Do a custom install and install the ESR version in its own program folder to use multiple Firefox versions.

• https://support.mozilla.com/kb/Custom+installation+of+Firefox+on+Windows
• http://releases.mozilla.org/pub/mozilla.org/firefox/releases/

Make sure not to start Firefox after the installation has finished. Create a new profile exclusively for that Firefox version. Create a desktop shortcut with -P "profile" appended to the target to launch each Firefox version with its own profile.

• http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
• http://kb.mozillazine.org/Shortcut_to_a_specific_profile
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox

I tried that and it's not working. If I could get a link to 14, since that was the last version I had that worked with my school, I would appreciate it.

You should be using the Extended Support Release version, which receives the same security patches as the full release versions receive while maintaining compatibility.

http://www.mozilla.org/en-US/firefox/organizations/all.html

You might want to notify your school's tech website about ESR, so that they stop telling their users to use outdated versions of Firefox which have known vulnerabilities, and leaving their users open to being exploited. Very irresponsible conduct, IMO.

You wrote above that version 3 (3.6) through 18 are supported, so the Firefox 17 ESR version should be working.

You did create a new profile for this version to have a fresh start?

Isn't the website loading at all or are only some features not working properly?