Shares of Koss Corp KOSS.O, BlackBerry BB.N and GameStop GME.N dropped between 2% and 5%. By Medha Singh June 4 (Reuters) - U.S. stock index futures were listless on Friday as investors were on the fence ahead of a crucial report that is likely to show jobs growth accelerated last month, possibly fanning fears over inflation and easing of the Federal Reserve's support. A stronger-than-expected reading could further stoke worries that the robust economic recovery could push the Fed to contemplate paring back its bond buying and raising interest rates.