I personally use IE, one, because its a standard i have come to use over a number of networks. I find it reliable, and, if i install another web browser as standard on my computer, i will inevitably have to explain to a number of computer-illiterate housemates how it is used (note words 'inevitably' and 'computer illiterate'), something i have no time, or stress capacity for.
While firefox may be the best browser on earth, IE is one of the oldest, and i have a penchant for Ancient technology

JMHO