OSLO (Reuters) - Norwegian mobile browser maker Opera Software's board is "not strong enough" and lacks ambition, a top shareholder said on Tuesday.

"The board lacks knowledge and that has to have consequences," Opera founder Jon von Tetzchner, who holds just above 10 percent of the company, told Reuters on the sidelines of the annual general meeting.

"I think this board shows lack of ambition," he said.

Shares of Opera Software soared last week on market talk Facebook Inc. was in discussion to acquire the firm for its advanced mobile phone software technology.

(Reporting by Joachim Dagenborg, writing by Victoria Klesty)