FireWire plugs only fit one way, just like USB. Yet, one of FireWire's advantages is that the connector doesn't have a fully symmetrical shape, that makes it more obvious how to insert the plug. Users don't even have to look, they can feel which side is narrowest or has a dent on one side (depending on the type of FireWire plug).
I should have made that wording clearer... by "like a firewire plug that is bidirectional (ie. not tapered)" I mean a symmetrically shaped firewire "style" plug, only with the same pins arrayed down each side... so no matter how you plug it in it's correct.
http://pinouts.ru/connector/4_pin,_6_pin_or_9_pin_IEEE1394_F...