What!? Opera has had by far the least known security issues of any browser:
Compare this:
http://secunia.com/advisories/product/33328/?task=statistics
To this:
https://secunia.com/advisories/product/2869...task=statistics
Now don't get me wrong, Mozilla does more frequently disclose vulnerability info- but the difference is pretty staggering. Opera has always been faster and more secure than firefox.
Hell the only thing firefox has ever *really* had going for it has been "Not being internet explorer" and "extensions"- aside from that it's been fairly mediocre.
Now to be fair, all other browsers now also have extensions- and it does look like Firefox is sort of going the right direction with 4.0 as well (Mostly in terms of not being disastrously slow).