>Firefox does take longer to fire up on my computer then IE 6. So far Firefox has not hung up. Just come back in two years and we can compare this "data" between IE and Firefox. As Firefox becomes more popular you might expect more attempts to break it from hackers.

Not necessarily. Apache server still has a lion's share of the web server market, and yet an unproportionally high percentage of the attacks goes against IIS, which is not that popular. I've read this (with hard numbers) in one of the articles linked from UT's main page a couple of weeks ago.