Snowfall will not cause that speed variance between different programs. If you are getting TWO different speeds at the same time using different programs, something is wrong with one of them. I am going to bet, in your case, it is firefox.
Now, there are several ways to fix this. Usually in these situations Internet Explorer is faster. I don't know why, but it is. I would try it. If it does not work, I would try a third one just to be safe. A good example is Opera. http://www.opera.com/
This MAY help, and I may be wrong. But that is my assumption.
Thanks,
Nanobot