Firefox 3.6.*Install View Source Chart 3.01
This version is sandboxed pending review by AMO, but you can still install it.

NEW FEATURES:
-Cursor changes to hand to indicate clickable areas
-Text inside containers is word wrapped
-Selected text can be DEselected (by clicking it) without collapsing a container
-Displays entire opening tag in titletip when mouse hovers over container. This enables view of opening tag/attributes from any hot area of a container. This is especially useful when navigating a deeply nested page structure.

"...the most accessible DOM inspector available to web developers."
"(This) extension should be standard in every web developer's toolkit."
John Resig, creator of the jQuery JavaScript Library, from his book, Pro JavaScript Techniques.

"this is a great quick debugging tool for me and a lifesaver of a learning tool for those i instruct. html is all about nested containers and this clearly shows them much better than all my commenting, indentation, or syntax coloring ever could."
Cheridy
Harvard University Graduate School of Design Instructor

"Even the most complicated nesting xhtml containers and hierarchies are so much easier to navigate that it's almost laughable."
Dewey Spencer

WHAT IS SOURCE CHARTING?
Source Charting is a User Interface useful for navigating HTML source code at lightning speed. It is also an excellent visual aid for those learning HTML.

A PICTURE SAYS A THOUSAND WORDS
Eyesight is the most efficient way for the human brain to process information. By placing visual boundaries where they already exist invisibly, Source Charting enables you to take in DOM structure and hierarchy as fast as your brain possibly can.

IT'S BETTER BECAUSE...
When we have to build invisible HTML boundaries *mentally* - usually made up of some devised series of manual actions (clicking, finding, reading, etc.) - we experience forced breaks in cognitive processing. As the DOM becomes more complex, more productivity is lost.

Source Charting is better because it eliminates the need for processing any other way but the fastest: visually.

ZOOM FEATURE
View Source Chart users can take advantage of a built-in browser feature (Ctrl + -) which results in zooming out of source charts. Now you can see more of the DOM than ever before! You don't even have to scroll as much. Sweet.

SUMMARY
Source Charting:
* Visuallly Defines HTML Tag Boundaries (so you don't have to )
* Visually Defines DOM Structure and Hierarchy (so you don't have to )

Source Charting allows a user to ...
*quickly scan and identify tags without reading
*gauge a tag's hierarchy rank just by looking to its side
*see more of the DOM in the view port by zooming out!

JUST A THOUGHT
The source charting concept can also be used as the basis for any User Interface design which attempts to depict containment such as file/folder viewing, website navigation, and last but not least, [your idea here].