On the other hand, Occidental Petroleum OXY.N, up 1.7%, led gains among the energy stocks tracking oil prices. By Devik Jain Dec 6 (Reuters) - The Nasdaq index was set for a lower open on Monday as mega-cap technology firms slipped and shares of Nvidia led declines among major chipmakers, while Dow futures were supported by a rise in economy-sensitive stocks. Wall Street's major indexes registered weekly declines on Friday, swinging wildly as investors digested Omicron news and Federal Reserve Chair Jerome Powell's hawkish comments about speedier taper to tackle surging inflation.