Well, this is interesting. I'm having a problem with the adb shell command on the Fire HD.
C:\adb>adb shell settings list system
usage: settings [--user NUM] get namespace key
settings [--user NUM] put namespace key value
settings [--user NUM] delete namespace key
'namespace' is one of {system, secure, global}, case-insensitive
If '--user NUM' is not given, the operations are performed on the owner user.
I am running adb on a Windows 10 machine with the tabled attached. The tablet has developer options enabled and Enable ADB is also enabled. There is no USB Option to set file transfer (MTP), but the tablet shows up in the Windows devices list and files can be transferred to the tablet via File Manager. Plugging my Galaxy S8 into the computer and running the "adb shell settings list system" command works fine. Any ideas?