How can I transfer files to a Kindle Fire with a Micro-USB cable?

The Kindle Fire is reported to connect properly out of the box by several users. Just plug it in and look for a "Kindle Fire" icon to appear in your launcher sidebar. If not, try the technical solution below:

The approach I would take would be to mount the Kindle and then you can cp files over in the terminal or likely even the file browser. I'd start with dmesg as you've done and note which device node the Kindle is put on. Look for lines in dmesg like;

[149600.320060] usb 1-6: new high speed USB device using ehci_hcd and address 13

or similar and you should see a line like this as well;

[149602.666223] sd 4:0:0:1: [sdb] Attached SCSI removable disk

If you look at the last line above, you'll see 'sdb' in brakets, that is the device node that the new USB device is attached too. You can confirm this with

sudo ls -l /dev/disk/by-id/

You should see something like this;

lrwxrwxrwx 1 root root  9 Jan  7 20:01 usb-Generic-_SD_MMC_058F63646476-0:0 -> ../../sdb

Of coruse you'll see something different because I doubt the Kindle will identify itself as a generic SD MMC device.

You can mount that device as root with this command;

sudo mount -t ext3 /dev/sdb/ /mnt/kindle/

(that assumes you've created a directory called "kindle" under /mnt)

You should be able to see the Kindle in your file manager now. And you can also use the terminal and cd to /mnt/kindle which should show you a mounted Kindle file system.

Note that I haven't actually tried this since I don't have a Kindle and I'm only guessing at the actual file system which you supply to the -t flag for mount, but I'd bet its ext3.