Greasemonkey is an extension for Firefox and other modern web browsers, that lets users write scripts to control how they see web pages. These scripts can improve the presentation of a website, cut out unwanted material, or add in totally new functionality. Some scripts only work on a single site or page, while others apply to all pages. For users who don't want to get to grips with Javascript to write their own scripts, userscripts.org shares useful scripts written by other people. Read more about Greasemonkey on Wikipedia.
I've written a number of Greasemonkey scripts, to help improve the Geocaching.com website and provide other useful geocaching tools:
- Enhancements to the Geocaching.com maps, allowing you to see caches on Ordnance Survey maps in Great Britain, and easily move between map and list views.
- Integration with Google Maps, so that you can go straight from Google Maps to a map or list of nearby geocaches, or see coordinates for the place you're looking at.
- Improvements to cache listing pages, to let you see download additional waypoints for a cache, see its height above sea level, rate it for accessibility or transfer its details to a smartphone via QR Code.