I tried accessing the 'Dominant 7th Chords' article under Music Theory using firefox (XP) and it doesn't recognize the plugin being used. I tried accessing the same page using IE and it prompted an install for 'Sibelius Scorch'. Looks like an activex component? Might be an issue if you plan on delivering lot of lessons using that.
It is an activeX component, but there is a Mac plugin that works under firefox on macs . . . so i'd think under windows it'd be fine.
In any case, the same data is available as a pdf from a link in the article.
Anyway a manual install of Scorch worked for Firefox. Cheers.
When you wanna rock hard children, lean on F sharp