FTSE 100 falls as U.S. uncertainty weighs

(Reuters) - UK shares opened lower on Monday, as multinational stocks tumbled on reports U.S. President Donald Trump privately discussed firing the head of the Federal Reserve and a partial U.S. government shutdown weighed on investor sentiment.The FTSE 100 was down 0.8 percent and the mid-cap index was 0.5 percent lower by 0828 GMT. The bourses were due to close early ahead of Christmas.Dragging down the UK's main index were companies that have a greater international presence, with Imperial..