Firefox isn't the most secure. In theory, the most secure would be a text based browser, but for all common purposes, it still isn't. Opera is more secure, and I do not like Opera, I use FF, but allow me to explain. Firefox is popular these days, so more and more bad people are starting to use it, and finding vulnerabilities, and there are a number of exploits out there for firefox, however, there are less than IE, and they are usually patched as soon as they are found. Opera, on the other hand, has had less exploits, becaue it's not such a center of attention, and while there may be just as many or more holes, people haven't found them yet, and you can safely browse without worrying about them being exploited. Am I saying Opera is more secure than FF, no. I believe FF is more well designed security wise, and overall (I don't like opera that much), to be a better browser, but with popularity it gets more exploited. I'd need to see source code to determine which browser is truely more secure, and Opera is closed source anyhow. So, bottom line, Opera is more secure due to it's less popularity. That doesn't mean there are 0 exploits out for it, however.