Originally Posted by sd_shadow
try formating sd card
Did that. Now Windows views it as a removable disk.
Update: adb devices gives my kindle in recovery. Trying to install an update.zip file (Fire OS 6.3.3 downloaded directly from amazon) gives:
Checking for MD5 file
Skipping MD5 check: no MD5 file found
file_getprop: failed to stat "/system/build.prop": No such file or directory
E: Error executing updater binary in zip '/sdcard/update.zip'
Error flashing zip '/sdcard/update.zip
updating partition details"