Chiming in to say that it works fine for me on FF on Mac OS X.
I liked your little pixel art monsters. Am I right that I was killed – multiple times – by a chicken's flying egg?
I chose GoGoSpace for the "A Game By Its Cover" jam as well!
Also, I wanted to add that it's nice to see at least one other Haxe user in the jam, though I used heaps.io instead of HaxeFlixel.