Stewarts Law picked a good time to drop this bomb. The firm filed a $15 billion, class-action suit against Facebook just as the company was preparing to trade its shares today, its plaintiffs claiming the company violated user privacy by allegedly tracking their Internet use. Stewarts and its plaintiffs are seeking is just $1 billion shy of the money Facebook is expected to raise in its IPO. The company opened on the stock market Friday at $42 a share, the third-largest IPO ever. The social networking giant has been hit with privacy suits in the past, most recently in March.