Tokyo stocks opened slightly lower Friday, tracking overnight falls on Wall Street, although the downside was supported by bargain-hunting after a plunge on the Nikkei index the previous day. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 53.11 points, or 0.13 percent, from Thursday to 40,073.24. The broader Topix index was down 7.65 points, or 0.27 percent, at 2,860.98. On the top-tier Prime Market, decliners were led by air transportation, pharmaceutical and insurance issues. At 9 a.m., the U.S. dollar fetched 157.15-16 yen compared with 157.31-41 yen in New York…