Debian see’s a Kindle Fire as a mtp device¹, so you have to mount it as jmtpfs /media/boudiccas/k2 where k2 is your device name, which then says -

##jmtpfs /media/boudiccas/k2
Unable to read MTPZ public exponent from ~/.mtpz-data, MTPZ disabledDevice 0 (VID=1949 and PID ...