Rated 4 out of 5 stars
I was always skeptical of Greasemonkey until I found an actual need for it. Now I love it.
I used to think there wasn't a need for me to use Greasemonkey. Many friends over the years would tell me about scripts they would run in their browser and how much better their browsing experience was due to Greasemonkey. I would try it when a new version would come out here and there. I never found it compelling enough to keep it.
Fast forward to today. I cannot imagine not using it! I wish I would have been less stubborn so I could have used this wonderful addon to it's full potential.
The ability to run user scripts is phenomenal. One of my favorite scripts is for YouTube. The Yays!-script will allow you to pause videos, automatically resize the width, and play them in HD just by loading the page. This is all possible due to Greasemonkey's ability to run custom tailored scripts with ease.
There are so many scripts out there, I'm sure if you're looking to do something with your web browser that it doesn't already do, there's probably a script out there to do said "something".
I really think you should give Greasemonkey a shot, it's super lightweight and easy to run. User-scripts are super easy to install and uninstall.
There's definitely something for everyone!