How did Firefox get on the machine?
Not sure.Perhaps this kid...or another kid.If it was an administrator or teacher you might have an entirely different story.
It is an easy free download. All you have to do is got to
http://www.mozilla.com/en-US/firefox/
They have a free one, and then they encourage you to upgrade (at cost?).
It is likely that the kid brought his own flash drive and plugged it into the USB port. The advantage is that you can run your own browser app, which retains your own personal links and history. So, if you are working on a school project and need to remember a link when you get home, you don’t have to write it out. Also, you can save all your personal work and keep it with you in a pretty secure format.
Of course, other advantages include the ability to bypass any security put on IE and IE itself for that matter. It is simply a bonus to make your teacher look stupid at your tech savvyness.
Can’t you run Firefox from a jump drive? That way you can take your Bookmarks, etc. with you?