Tutorials

A long time ago I installed Greasemonkey and with the latest upgrade it survived after transition to Firefox 3.0.
Greasemonkey allows you to run javaScripts that you created yourself on somebody else's sites. That's the short explanation. Anyway, the script does not need to be included in the source as you might expect from a normal javaScript. You may want to change the background colour or the font size of an arbitrary site you often visit. Those are common uses, together with removal of certain elements most notably adds. You can completely restyle a webpage.
The main site Greasespot holds a huge collection of scripts. Installing a script is easy. If Greasemonkey is installed you only need to click the link to the Greasemonkey script to trigger an installer. You will see at the end of this post how that goes. Unfortunately I didn't find the Killer App there. I don't believe there is. So the use of Greasemonkey is in practice limited to things you make cy yourself. Luckily the huge script library is of great help there. You are bound to find a script that does 'almost' what you want.
In the Greasespot site you find a link to the Open Source (downloadable) book Dive Into Greasemonkey which is an excellent guide to get started apart from the fact that most of the examples don't run. The book is simply outdated. But worth a glance anyway.

For the B2evolution forums I wanted some hacks. One of them is available as Greasemonkey script. That is phpBB No Stretch. If a post contains a code with a very long line as can be the case with an URL the post itself becomes very wide rather than wrapping rhe long line. The phpBB No Stretch plugin for Greasespot does just that. It wraps the long line.
A very impressive plugin is IMDB Pirated Version It adds a bar with links to torrents of the particular movie from the page you're at. Have a look at this picture:

The line just under the film title is added by the script. If you click it it Ajaxes to the sites it gets its information from. Actually, this is a kind of Killer App.