[shamanNS]

@oioioibaka You can't register the device while it offline, it needs an Internet connection for that.
To avoid firmware update getting completely downloaded while you're typing in login information what you can do is be quick while doing the registration + turn of WiFi as soon as your done + intentionally use a slow Internet connection ( switch your phone to 2G only signal > turn on WiFi hotspot on your phone > connect your Kindle to that hotspot signal instead of connecting it to your home router) + when finished with registration connect your Kindle to a computer via USB cable and make sure to delete the "update.partial.temp" file (or whatever is the filename Amazon currently uses) like @DNSB said.