I am not aware of French relgulations regarding protests, but in my country (Poland) to make protest legal you only have to inform authorities some time before (1 week?), state number of expected participant and so on. Sometimes you are told you have to limit your protest to certain area, e.g. one line of the street (if it's a march) so that cars would be able to pass. It is not very difficult to legalize demonstration in Europe, believe me.