I had some water damage and my USB ports do not work anymore and I was wondering if there is a usb adapter that I can plug into the firewire slot so I can have a usb connection? I have a Mid 2010 15"
Nope. You'd need a converting breakout box or something and it would be spendy so no one makes them that I know of. Each separate protocol is relatively cheap to implement. A converting of the 2 techs has little motivation.
I am surprised that the USB controller id the only thing that went south for you but maybe you can get a USB port via the card reader? Not sure. But on a laptop yes, new motherboard. Or maybe Apple can fix it for a smaller fee. I'd take it into an Apple Store to see. It is free to have them look at it.