A lot of facebook plugins listed below don't work, but as I suggest that facebook is a crap, I don't really use facebook a lot, and so I didn't test all of them. Just the part. And I didn't research that stuff a lot.

Installing Facebook script plugins 

Greasemonkey is a Firefox extension that allows you to customize the way webpages look and function.

1. You may want to view official Userscripts help on GreaseMonkey add-on.
2. Install GreaseMonkey add-on.
3. Get on some script's page.
4. Press Install.
5. You may need to setup the script. If so, and you are confused - go to step 1.

Scripts

Following add-ons are GreaseMonkey plugin that enables installation of scripts, that are listed below and the scripts themselves. So here's what you need to do (if you want, of course).

Facebook colour changer
Gives options for changing Facebook color scheme to what you want it to be using a color selector.

In your Facebook
Zooming avatar pictures - larger versions of thumbnails and profile pictures on mouseover on Facebook.

Facebook: Cleaner
Deletes ads - this script removes many ads and updates that unavoidably appear on your Facebook pages.

Bearable Facebook Wallpost
Makes the Facebook wall-post comment section textbox biugger, lengthening and widening it to the width of an actual post.

Facebook Notes QuickEdit
 Easier note writing - adds shortcuts for formatting Facebook notes.

Remember that facebook addons, plugins and scripts only change the way facebook looks on your own computer.