What a surprise Virtual Box have regressed to preventing USB from working again. They should have left it as adding the user to the vboxusers group (which you still require), but oh no!
Now you have to do the following on FC to make USB devices available to you;
Since we of the Fedora world have to use the install script it means our Virtual Box is installed into /opt/VirtualBox
In this directory there is a script called VBoxCreateUSBNode.sh
Edit this script and look for the following code;
if test "$class" -eq 9; then
exit 0
fi
Comment out these lines so it looks like;
#if test "$class" -eq 9; then
# exit 0
#fi
Then go to /proc/bus and you need to allow rwx to all users;
chmod -R 777 /proc/bus/usb
(This is still a work in progress, and ideally you should make the directory group something like vboxusers and then do chmod -R 775 /proc/bus/usb to make sure that only those you trust have access.
Now start VirtualBox
Start your VM
And you should now be able to select your USB device.