Jakub Voracek had two assists, and Giroux also had an assist to help the Flyers snap a three-game losing streak and extend their home winning streak to six games. They were coming off a 2-3-1 trip in which they finished up 0-2-1.
Mason shut the Canadiens out for 59 minutes before Alex Galchenyuk scored with 55.1 seconds left to cut it to 2-1.
The Canadiens have lost two in a row after going 9-0-1. They followed a 6-0 loss at home to the Los Angeles Kings on Tuesday with another offensive clunker.
The Flyers didn't show any ill effects from a 13-day trip. Despite a 7-2 loss at Chicago on Wednesday, they looked fresh from the start.
Raffl gave Philadelphia a 1-0 lead in the first period with his second NHL goal. Voracek set it up with a perfect pass from behind the net to Raffl in the slot. He wristed a shot over goalie Carey Price's glove into the top corner.
Raffl didn't score in his first 17 games, but has two goals in three games this week.
Another crisp pass from Voracek set up Philadelphia's second goal. Brayden Schenn took the puck up the middle, and he passed it to Voracek skating down the left side. Voracek sent a crossing pass to Giroux coming down the right wing, and he beat Price with a slap shot.
Danny Briere, a fan favorite during six seasons with the Flyers, returned to Philadelphia for the first time since his contract was bought out last July. Briere got a standing ovation during a video tribute in the first period and he waved to the crowd from the bench.
The Canadiens had a goal disallowed in the third period because Brian Gionta pushed it in with his hand while sliding headfirst into the crease.
NOTES: Mason had 10 shutouts for Columbus when he was the NHL's top rookie in the 2008-09 season, and 10 more in the last five seasons. ... The Flyers scored first for the fourth game in a row. They were 0-2-1 in the other three. ... Giroux has five goals in 13 games after getting one in the first 19. ... Canadiens D Alexei Emelin was ejected for elbowing Steve Downie late in the second period. ... Canadiens lost consecutive games in regulation for the first time since Nov. 1-2.