I threw together some quick proof of concept code to show how extension dependencies could be graphically represented using the Graphviz tool. Script requires you to have installed the perl5 and graphviz extensions. At the top of the script you can specify the path to your onboot.lst file (or any other text file that contains a list of extensions you want to graph), and you also specify the path to your tce/optional directory.
Attached to this post is a PNG that the script produced showing dependencies for Firefox and a couple of other small extensions.
Perl script is attached to post as well.
Brian