Just a personal reaction, I think lopping would spoil the shape - why not consult a qualified tree surgeon for advice? Beware of the unqualified who sometimes just wade in and lop, with horrible results)

I would not top it--as Seragram says, it makes the tree look horrible. Is there some reason why you are afraid of the tree falling? Most Fir trees are quite firm in the ground, and won't grow where the soil is swampy. A skilled tree surgeon would be able to thin it out artistically, to reduce wind resistance, if there is some doubt.