Hundreds of protesters marched for a second straight day Saturday through several working-class districts of Ajaccio shouting slogans such as "This is our home!" and "Arabs get out".
Hundreds of people defied authorities on the French island of Corsica Sunday to rally in opposition to the influence and presence of Arabs.
On Sunday, the demonstrators marched through several neighbourhoods in Ajaccio, but did not go to the Jardins de l'Empereur area - the scene of Friday's attack.
Two men in their 20s were held in custody as part of a probe into the unrest.
Regional official Francois Lalanne said a fire had been deliberately lit in the neighbourhood in a ruse aimed at "ambushing" the emergency services.
Once they arrived, a group of about 20 people "armed with iron bars [and] baseball bats" attempted to break through the windshield of their truck, according to a firefighter who was interviewed on French television.
Two separate investigations were opened, one into the attack on firefighters Thursday and the other into the damage to the prayer room Friday, he said on iTele TV station.
On Friday, 600 people gathered in front of the police headquarters in Ajaccio in a show of support for the police and firefighters.
French Prime Minister Manuel Valls wrote on Twitter that the break-in to the Muslim place of worship was "an unacceptable desecration", condemning the "intolerable attack" on the firefighters, and calling on Corsicans to respect the law of the Republic.
"This behavior must stop".
Jean-Guy Talamoni, president of the Corsican assembly, said the anti-Arab violence was "totally incompatible with our political tradition and culture".
Nationalist parties won control of the region for the first time this month but Simeoni insisted there was no connection with the "outbursts of hatred", pointing out that there had been "gestures of solidarity", including young people going unbidden to help fix the prayer room.
Tensions were high on the Mediterranean island, widely known in France as the Isle of Beauty.
The Christmas violence came amid heightened security measures for the season in France after the November 13 attacks by jihadists in Paris that killed 130 people.