I am using MarketPress, Hummingbird and WP Super Cache. I found this on the MP product page:
Note on caching If you are using a caching plugin such as W3 Total Cache, or have another caching mechanism such as Varnish enabled on your server, you’ll need to add a couple of cookie exceptions for MarketPress to function correctly: PHPSESSID mp_order_history_ mp_session mp_globalcart_*
Is Hummingbird aware of the need for these exceptions? How do I add them. Same questions for WP Super Cache.