I generally travel with a backpack that I shove under the seat in front of me. Among its other uses, it serves as a footrest. It's larger and more obtrusive than a single-purpose footrest would be. I don't specifically remember how I used it in flying AF BOS-CDG-AMM last year, but the odds are that I had it. No FA, whether on AF or any other airline, ever had the slightest problem with it. (None of them ever asked me where I got it, either, but places that sell backpacks are not exactly hard to find.)