From the UniverseView website:
- Download & Install the greasmonkey add-on -> addons.mozilla.org
- Go to the download page -> UniverseView Download
- Click the Userscript button
- Download the script
- Drag it from the download location into firefox
- Accept the installation
From userscripts.org:
- Download & Install the greasmonkey add-on -> addons.mozilla.org
- Go to the userscripts website -> userscripts.org
- Click the install button
- Accept the installation