That is just not true, it's quite easy to fire somebody in France, you just have to pay correctly for settlement.
It's possible to fire people without justification and the company will be brought to court. There is a new law from Macron that caps the damages the employee can get to pretty much nothing when he only has a few years of tenure or less. You could provision for a few months of salary.
(I’ve hired and run large engineering offices in France and in the US).