Looks like that page has gone. I did find a forum post referencing it:
It seems to indicate editing the whphost file and making some height 100%.
I have the EXACT same problem when viewing Webhelp through Firefox. Like you, webhelp does not display the left TOC panel 100% and displays scrollbars, even when expanded. I uninstalled it, upgraded, and did whatever I could to get my file to display the TOC correctly in Firefox.
On an interesting note, the left panel displayed correctly during a quick test using other computers; I just assumed it was something with my computer. I currently generate the output as DHTML > Pure HTML.
I'm sorry I can't give you a solution, other than to acknowledge the same issue still occurs with me using FF: http://forums.adobe.com/thread/586176 . It displays okay in IE8, not in FF 3.6.3.