Firefox only (Windows/Mac/Linux): Greasefire is a companion extension to the popular Greasemonkey extension designed to help you customize your web browsing by finding user scripts for any page you're currently visiting.
Once installed, the extension automatically searches the popular Greasemonkey script repository Userscripts.org for scripts related to the site you're visiting; if a script is available, the Greasemonkey icon in your Firefox status bar will display a fiery background to indicate that it found matches. For Lifehacker, as you can see from the photo above, Greasefire found nine matching scripts.
From there, installing new scripts is simple. Just click the "X scripts available" entry, then browse and find a script you like in the pop-up window. Click the install button at the bottom of the window when you find something you like.
If you've never been able to get into Greasemonkey beyond our top 10 Greasemonkey scripts, Greasefire is a great tool to discover new user scripts and customize your web with Greasemonkey. Greasefire is a free download, works wherever Firefox does.