I made the same mistake the first time I mounted a pair of Panaracers. I'm a bit anal about everything fitting the way it should on my bike so I took the stupid thing off -which is completely unadvisable when you're dealing with new UST tires...ouch! - and put them back on the right way.

One thing to note about the Fire XC Pros: they are semi directional. Look at the outter tread and notice that there is a small ramp up to the main knob which is put there to help reduce roll resistance. If you're a hardcore XC guy, you may want to re-mount the tires because, having them reversed, will slow you down just a teensy, tiny bit. On the other hand, mounting them backwards will likely help increase your traction to some extent so you may like that better.