The new Kindle Fires can only be managed via a protocol known as MTP, but you can still mount them.

First make sure you have mtpfs installed.

sudo apt-get install mtpfs

Then, since udev and libmtp do not yet know about Kindle Fire do :

lsusb

My Kindle Fire HD shows up as "Bus xxx Device yyy: ID 1949:0007 Lab126"

What's important is the USB ID.

Next, add a file to udev to recognize your device:

sudo vi /etc/udev/rules.d/51-android.rules

Add this line to the end, substituting your USB IDs you figured out above if they are different:

SUBSYSTEM=="usb", ATTR{idVendor}=="1949", ATTR{idProduct}=="0007", MODE="0666"

Connect your Kindle and look to see if the system found it:

dmesg

In the spam you should see something like this:

...

[32421.676671] usb 3-1: >new high-speed USB device number 4 using xhci_hcd

[32421.702240] usb 3-1: >New USB device found, idVendor=1949, idProduct=0007

[32421.702247] usb 3-1: >New USB device strings: Mfr=2, Product=3, SerialNumber=4

[32421.702250] usb 3-1: >Product: Kindle

[32421.702254] usb 3-1: >Manufacturer: Amazon

[32421.702257] usb 3-1: >SerialNumber: xxx

...

If you couldn't find your device with lsusb, you can get the identifiers here too, but when you edit the udev rules you'll have to disconnect and reconnect.

Now let's make a place to mount it.

sudo mkdir -p /media/Kindle

sudo chmod 755 /media/Kindle

Also, it doesn't hurt to make sure fuse is set up to allow regular users to mount things.

Make sure /etc/fuse.conf is set up for this:

sudo vi /etc/fuse.conf

Look for the line that says "user_allow_other" and make sure it is uncommented.

Almost there! This part will be automatic from now on. All we have to do is mount it now.

Plug it in and setup the MTP over USB connection by mounting it, like this:

mtpfs -o allow_other /media/Kindle

Be patient with it, it's not the fastest thing ever. At any rate, once this command completes, you should see a kindle file system in Nautilus, etc.

When you're done using it, for example I load music into /media/Kindle/Internal Storage/Music, or use the ebook tool Calibre,

sync

fusermount -u /media/Kindle

I drop these commands into aliases, but you can just as easily add a "RUN=" to the udev rule or stuff them into shell scripts.

I prefer the Android app "ES File Explorer" to wander around and look at files on my Kindle... because Kindles are not good at "auto-discovery" of new files.