Oil firms including Exxon Mobil XOM.N and Chevron Corp CVX.N fell 0.3% as a rally in crude prices petered out. By Devik Jain Sept 29 (Reuters) - A rebound in beaten-down technology shares set U.S. stock indexes on course to open higher on Wednesday after concerns about inflation and rising Treasury yields sparked one of Wall Street's worst selloffs this year. Wall Street ended sharply lower on Tuesday in a broad sell-off, with the benchmark S&P 500 index .SPX logging its biggest one-day percentage drop since May and the Nasdaq posting its worst daily selloff since March.