First let me say that I love H3Viewer and I really appreciate the time you've taken to work on it in the absence of a unified help browser for Visual Studio 2010.
I just updated from 18.104.22.168 to 22.214.171.124, and the default font size for the TOC is significantly smaller. I'm in a normal en_US locale, if that matters. I don't see any way in the menu items to increase the font size for the TOC, only the font size for the active page.
This is a really big deal for me, I prefer to browse for help over searching, so I spend a lot of time navigating the TOC.