Facebook Shares Jump 8 Percent

A former critic of the stock's performance is now more optimistic

One of Facebook Inc.'s original bears has done an about face.

Bernstein Research, which was downbeat on Facebook after the social network went public in May, is now recommending that investors buy Facebook shares. Bernstein boosted its investment rating to "outperform" from "market perform" on Monday, saying Wall Street may be underestimating Facebook's revenue growth potential over the next 12 to 24 months.