Aha! I *finally* figured out how to have my Firefox extension get the Meta tags from the current webpage:
allMetas = window._content.document.getElementsByTagName("meta");
for(var i = 0; i < allMetas.length; i++)
if(allMetas[i].name == "METATAG")
// do something with METATAG
THAT was annoying. Now I can finally finish up the ICBM/geo.position firefox extension.