I use Firfox becuase of the better speed on my dialup and its nice graphics and flexibility.
I also love the fact that in the "Favorites" folder it keeps the original site symbols instead of IE pirating them and converting them all into Microsoft generic folders.
Firefox is more theme versatile (Hate cats but love the red cats green flavor theme). It is also not bound so intregally into the OS. Big problem---delete Firefox and download it again.
I also use IE and some times use both browsers simultaneously.
That said, I also think that Microsoft has been maligned a bit unfairly. Of course all the hackers are going to attack the most widely-used browser. Microsoft has been timely and consistent with providing patches.
So do I on a regular basis. I like certain features on each of them.
And I agree with IE being embedded too deeply into the OS, it's something MS made a big mistake in doing.