I told you that it is not a problem of Fedora. I updated mine and it works. If we do have more information we can help you better.
Can you please do this to get more information about your system? :
First, please reboot your computer, then restart your mobile phone and just then switch on usb tethering, and last connect it to the computers usb.
I see above your Motorola just works on usb2 ports, is this right? Was this always so?