First up, Free is the name (Free Mobile) of a mobile provider in France. And the word for "free" in French is gratuit. Free in this case is mobile without limits, not free to use.
Most tourist areas of Paris have free to use wifi (the city will list them under Paris_Wifi_####, or WifiLib will have free connections with the creation of an account). You will also see that all of the major providers (SFR, Bouygues, Free and Orange) have open wifi spots too. If you know someone before you come to France, and they can give you their log in for these, more power to you. But if you don't have a login you're going to have wait and find a connection elsewhere. Most cafes have gratuit wifi, as well as the chains; Mc Donald's, Starbucks, Burger King (Quick does not), and you'll also find them in certain areas of Paris. For instance the entire Champs Elysees has wifi accessible by supplying an email address. French libraries (bibliotheque) also provide free internet.
This site lists the free spots provided by the city: https://opendata.paris.fr/explore/dataset/liste_des_sites_des_hotspots_paris_wifi/