Boston--In a move reflecting the moribund Wall Street environment, brokerage firm giant Fidelity Investments has shed 760 jobs, or 2% of its work force. Seventy of the jobs were cut in Fidelity's institutional or b-to-b unit; the rest were scattered throughout the firm. Fidelity, a privately held company known for its competitive culture and superior earnings abilities, is amid its grimmest season since the early '90s recession. Last July, it fired 160 institutional employees, or 9% of its b-to-b work force. Fidelity's biggest rivals, Putnam Investments Inc. and Janus Capital Corp., have also recently pared staff.