Fwd: Fan speed going up and down?

[christopher marlow]

Hi,

I have installed F20 Mate for the first time and have been using it
for 2 or 3 days now, and when opening Firefox the fan picks up speed
and gets faster, slower, faster, slow. But it seems like when I close
FF the fan goes back to a normal lower speed? Why is that? Is this
normal?

Thanks,
Christopher