The women - one of Algerian origin, the other Tunisian - leapt onto the stage and exposed their upper bodies daubed in slogans as two imams debated whether it was permitted for a man to beat his wife, according to Femen spokesperson Inna Shevchenko.
In fact, one of the speakers had just stated that the Prophet Mohammed "did not beat his wife or insist that she wait on him", as video on the Buzzfeed site shows.
A video posted on YouTube shows the women shouting "Nobody subdues me, nobody owns me, I am my own prophet!" in French and Arabic.
Stewards bundled them off the stage and handed them over to police, who detained them briefly before releasing them overnight.
Some of the audience shouted "Dirty whores, kill them" and about 15 men jumped onto the stage and assaulted them before the police intervened, Shevchenko told the AFP news agency.
The organisers intend to take legal action, according to police.
On Sunday afternoon a small group of self-styled pro-secular campaigners demonstrated outside the salon.
Before it opened a web petition called for the event to be banned, claiming that it would be attended by "fundamentalist preachers such as Nader Abou Anas, well-known for having endorsed rape in marriage and more widely the subjection of women".