Basically, French Extension is sort of building on the skills learnt in the Continuers - but much much more in depth. You learn to interpret opinions, and talk more about the world and stuff in it (unlike the Continuers which is totally based around me me me me).
It's more about expressing opinions, interpreting them, current issues, the world, more on French culture and the Francophone world etc... the big topic is (I think!) "The Individual in Society", and there are 3 subtopics (prescribed issues I think is the term) "Belonging versus Alienation", "Coping With Change" and "Tolerance of Difference".
All these themes are studied through a prescribed text, which is a movie. The two set movies are "Marius et Jeannette" and "Au revoir les enfants", but you only do one of them (I do M+J).
Then we tear the movie to pieces and examine the cultural stuff and discuss the issues, like class structures and differences in "Belonging...", big changes in your life, like romances and moving away for tertiary study in "Coping with Change" and religion and different cultures/etc in "Tolerance of Difference". (these examples in reference to "Marius et Jeannette).
Together with the movie, you would have to find for yourself news and current events-y type stuff on the net to read, listen to and observe so that the stuff we study can have really up-to-date relevence.
For me. I really like it. It's sort of like the advanced course in English, esp. the modules, but not... The toughest thing I find is expressing opinions, which I don't really do naturally, and in French it's even more difficult! But if you're good at French, it'll be a great option. But it's a LOT of work, which sort of hit me, kind of surprising for just a one-unit course... but it's fun.
Bonne chance avec tes études de français!
Chépas