Boston won its sixth in a row. It was the Bruins' highest-scoring game of the season and their most lopsided victory.
With 47 points, the Bruins have the best record in the Eastern Conference. The defending Stanley Cup champions have climbed back to the top of the conference after opening the season with a 3-7 record.
The shutout went to Tuukka Rask, his second in as many appearances and the 10th of his career. Rask made 30 saves after blanking Los Angeles Dec. 13.
Marchand scored Boston's first goal and its last two. His shorthanded tally 5:56 into the contest began a four-goal opening period that also featured scores from Milan Lucic, Benoit Pouliot and Dennis Seidenberg.
Gregor Campbell and Patrice Bergeron scored in the second and Marchand added two more in the third. Marchand also assisted on the goals by Seidenberg and Campbell.
Jose Theodore allowed four goals on 14 shots before being removed after the first period.
Scott Clemmensen stopped 17 shots the rest of the way. Florida has dropped three in a row.