China's biggest solar firms fired nearly one-third of their workforces last year, a Reuters analysis of company filings shows, as one of the industries hand-picked by Beijing to drive economic growth grapples with falling prices and steep losses. Longi Green Energy, Trina Solar, Jinko Solar, JA Solar, and Tongwei collectively shed some 87,000 staff, or 31% of their workforces on average last year, according to a Reuters review of employment figures in public filings. The job cuts illustrate the pain from the vicious price…