Connecting a Bootable External hard Drive

I am looking to add a bootable hard drvie to my macbook pro (13" retina display early 2015 model). I have read that bootable disks must be connected to firewire but the macbook does not have a firewire port. Is it possible to boot from a disk connected by Thunderbolt? (or a firewire connected device through firewire - thunderbolt adaptor)? Thanks for any help anyone can give.