(Adds Rio de Janeiro protests, Rousseff comment; Less than a month before the tournament kicks off, and four months before a presidential election, Thursday's protests will gauge the ability of demonstrators to once again rally frustrated Brazilians and the competence of police to manage unrest that occasionally escalated over the past year into violence and vandalism. A main thoroughfare was blocked with burning tires in Brazil's biggest city of Sao Paulo and protesters stormed a building in the capital Brasilia. Marchers in Rio de Janeiro blocked traffic on the two main streets in the city center. More...