Take a look at some of Friday's midday movers:
Tesla - The electric-car maker continued to fall on news of a third fire in six weeks of one of its Model-S vehicles.
Twitter fell on its second trading day after Hudson Square Research initiated coverage with a sell, and Pivotal Research downgraded shares of the short-messaging service to a sell from a buy rating on worries the stock had gotten too expensive.
Riverbed Technology rose after an affiliate of hedge fund Elliott Management disclosed a 5.8 percent take in the network-equipment maker and pushed for a strategic review.
Cablevision Systems fell after the cable operator lost more video subscribers than expected in the third quarter and showed a surprise loss of broadband subscribers.
Deere fell as Bank of America/Merrill Lynch downgraded the stock to neutral from buy, saying falling corn prices could impact future sales of farming equipment.
Fairway Group Holdings rose, rebounding from a 22 percent slump on Thursday after posting weaker-than-expected quarterly results.
Snap-On rose after the maker of tool-and-diagnostic equipment increased its quarterly dividend 16 percent to 44 cents a share.
Horizon Pharma surged after the specialty drug company posted a narrower-than--expected quarterly loss on strong sales of an arthritis treatment.
Tremor Video fell after Jefferies and Canaccord Genuity downgraded the provider of online-video advertising to hold from buy after it reported lower-than-expected third-quarter results.
Universal Display surged after the LED supplier reported a surprise quarterly profit and better-than-expected revenue. It also forecast better-tha-expected full-year revenue.
Arena Pharmaceuticals gained after it said Japanese drug maker Eisai will sell its diet pill in most markets worldwide.
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—By CNBC's Rich Fisherman.
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