NEW YORK ( TheStreet) -- Facebook ( FB) shares dipped 2.19% to $27.64 before market open Tuesday after the social networking phenomenon received a downgrade from Bernstein Research. The analyst firm downgraded Facebook to "market perform" from "outperform," citing uncertain potential upside for the stock, according to CNBC. Facebook shares closed down 1% during the previous trading session. The Menlo Park, Calif.-based firm was also the most active premarket Nasdaq stock on share volume of 525,982. Zynga ( ZNGA), however, continued its recent momentum, gaining 1.63% to reach $3.73. Shares of the social gamer have been on a tear recently, closing up 7% on Monday, boosted by last week's strong fourth-quarter results and the possibility that New Jersey could legalize online gambling. The San Francisco-based firm was another active premarket Nasdaq stock on share volume of 419,196. BlackBerry ( BBRY) slipped 0.25% to $15.69 on share volume of 124,859. NetApp ( NTAP), which reports its fiscal third-quarter results after market close on Wednesday, rose 0.76% to $35.63 on share volume of 90,200. Shares of Apple ( AAPL) slipped 0.24% to $478.80 before market open on Tuesday as CEO Tim Cook prepares to take the spotlight at the Goldman Sachs Technology and Internet conference. The Apple chief's comments at the San Francisco event will be closely monitored by investors, particularly following hedge fund manager David Einhorn's decision to sue the tech giant. The Greenlight Capital president wants his fellow shareholders to vote against Apple's proposal to do away with preferred stock, which he said restricts "the Board's ability to unlock the value on Apple's balance sheet." Apple shares closed up 1.04% during Monday's trading. TheStreet will be live-blogging Tim Cook's keynote, starting at 9:45 a.m. EST. --Written by James Rogers in New York. Follow @jamesjrogers >To submit a news tip, send an email to: firstname.lastname@example.org.