Here's a library to manage CSS class names on DOM elements.

Simple chatting script to be placed on a corner of a website
Also a good example how to use ajax.

List all plugins installed in FF

Flexible sorting algorithm based on Quicksort with extra functionality, such as:
- Direction (ie: ascending or descending)
- Sort-by-path (eg: item.name, item.name.firstName or item[5])
- Sorting function (returns true if two items are already sorted)
- Type checking
- All constants and support functions are members of the Sort() function
- Testsuite with hooks for cscript and in-browser javascript, so you can tweak and optimize, and make sure it still works
- Environment agnostic (can use with, say, SpiderMonkey or .Net's jsc)

Set a word or phrase in an input field, clear it onfocus

Delete a Cookie

This shows how the computed style of each node differs from the computed style of its parent. The root element, which has no parent, is instead compared against the root of a blank HTML document.

* create a new bookmark called "compute styles" in your firefox toolbar. Place the snippet code in the location field of your "compute styles". click the compute styles bookmark, then click an element on the page with the crosshairs.

Given a PHP array (even a deep nested array), returns a string representation of that array as JavaScript array. Useful when using PHP to output JavaScript.

It works with Array types. The example is a simple list of numbers, but the array could contain anything; lists of strings, functions, DOM nodes, whatever. Unfortunately, a lot of things that seem like arrays in the DOM aren't really, so you can't shuffle the images on a page with just document.images.shuffle() all by itself.

Allows you to hide all elements on an HTML page by their tag name. Extremely handy in getting around the "Windowless Elements" problem in IE, which is a bug that puts certain elements, most commonly select boxes, on top of any other element, no matter what. As you can imagine, this causes real problems with DHTML drop-down menus and such like. This is the simplest and quickest fix I've come up with, I simply set this function to run alongside the drop-down and all of the select tags vanish before a menu drops, then I run the show function when the menu retracts.