I signed up to try Webflow. Unfortunately Firefox is not supported. I guess the "Only works in Chrome" really is the new "Works best in IE6".
You can vote for this issue on our Wishlist to help get Firefox support prioritized on our roadmap: https://wishlist.webflow.com/ideas/WEBFLOW-I-17
(Fwiw the published sites from Webflow do fully support Firefox, just the Designer itself does not.)
http://www.bbc.co.uk/programmes/b006r5ck
the full series is available from the usual places.
So yeah, right now we have soft support for Firefox and definitely want to move that to official support, especially now with Firefox gaining much deserved momentum.