I'm a US citizen. I was in France for 9 months with a student visa that expired this past July. I also had a "titre de séjour" (residency permit) that has expired. In March, I might return to France for around 10 days for work (and possibly a couple days for vacation to Switzerland). Would I need a visa since I will have spent over 90 days in France in the past 12 months?
No. Time spent under a long-stay visa or titre de séjour does not count in the 90/180 calculation. Anyway, since it's 90 days per 180 (not per year), and you've been outside the Schengen area for more than 90 days, your current limit in the Schengen area is 90 days.