U.S. markets opened the first full week of 2014 trading to the upside but a duo of downgrades are weighing on two familiar names. Twitter shares are lower on the back of a downgrade from Morgan Stanley. Morgan Stanley says Google and Facebook are better positioned to take advantage of online ad spending. First Solar received a downgrade to "sell" from Goldman Sachs. Meantime Liberty Media is making a big to acquire the remainder of Sirius that it doesn't already own. And, Zynga says it will start accepting Bitcoin for some of its products.

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