World stock markets fell Friday, slammed by ratings cuts for Greece and five of its banks, which were announced ahead of a crucial Group of 8 summit this weekend. While Facebook's much-anticipated initial public offering provided a temporary distraction for traders, its first-day performance concluded with more of a whimper than a bang.

Facebook Inc. (Nasdaq: FB) shares, priced Thursday at $38 apiece, opened Friday at $42.05, but fell back to the IPO price within the first half hour of trading, before closing slightly higher at $38.37. Underwriters stepped in to support the price, the Wall Street Journal reported, citing people familiar with the matter.

On Friday, Fitch Ratings lowered its ratings on five Greek banks close to default territory. The move came after the firm cut its ratings on debt-crippled Greece Thursday to CCC from B-, as it warned, In the event that the new general elections scheduled for 17 June fail to produce a government with a mandate to continue with the [European Union-International Monetary Fund] program of fiscal austerity and structural reform, an exit of Greece from [the Economic and Monetary Union] would be probable.

Stocks. European stocks ended their worst week in almost eight months, with the Stoxx Europe 600 index falling 1.14 percent, to 238.88, its lowest close since Dec. 21. Asian markets also fell heavily, with Japan, Hong Kong, and Australia all hitting four-month lows. In the U.S., the Dow Jones Industrial Average and the S&P 500 suffered losses for the third straight week, their longest weekly losing streak this year. The tech-heavy Nasdaq gave up 34.90 points, to close at 2,778.79. Social-media companies were hit by Facebook's IPO, with Zynga Inc. (Nasdaq: ZNGA) plunging 13.42 percent, Pandora Media Inc. (NYSE: P) falling 7.13 percent, Groupon Inc. (Nasdaq: GRPN) dropping 6.69 percent, and the LinkedIn Corp. (NYSE: LNKD) dipping 5.65 percent.

Bonds. Cautious investors flocked toward the safety of U.S. government bonds. Treasury prices logged another week of gains Friday, with benchmark 10-year note yields recording a ninth straight session of losses. Meanwhile, the cost to insure Spanish government debt against default hit record highs Friday, a day after Moody's cut its ratings on 16 Spanish banks.

Commodities. Gold futures continued to rebound Friday, rising 1.1 percent, to $1,591.90 an ounce. July silver ended the day up 2.5 percent, to $28.72 an ounce. Copper settled down 1 cent. Oil futures slid for the sixth session in a row, settling at their lowest level in nearly seven months. Meanwhile, natural-gas futures climbed 2.2 percent.

Currencies. The U.S. dollar weakened Friday after its longest rally since at least 1985. The IntercontinentalExchange, or ICE, U.S. dollar index, a measure of the greenback's performance against a basket of six major global rivals, fell 0.47 percent, to 81.15. The euro was down 1.2 percent for the week, its third weekly decline in a row. The British pound was little changed, while the Swiss franc gained.