Rated 5 out of 5 stars
Scriptish is pretty much the ultimate user script engine. I can use Scriptish to run user scripts (special scripts that change how webpages work) much faster than Greasemonkey. It works very well in combination with Greasefire.
I like the flexibility of user scripts, given if one doesn't quite work how I want, I can change it! There are thousands of user scripts on the Internet, and if you want a user script that doesn't exist, you can make it and share it with the world!