Got my replacement Fire today. Looks like a brand new one, rather than a refurb. Wow - a big difference! The micro usb port makes a very tight connection without any play when I plug the charger in. I'm not sure whether the older one felt this tight when I first got it - it may have gotten progressively loser without my noticing it.
Comparing the two usb ports closely (on the old KF and the new one), the older one is recessed at least 1/32" deeper into the case than the new one. The old one doesn't feel loose, but there's significant 'play' in the plug when I plug a male connection into it.
Amazon is giving me 30 days to return the old one, which gives me plenty of time to set the new one up.