[Fire TV Q&A, Help & Troubleshooting] Determined:
The problem is that adb is accessible over IP only (or at least I have not yet found other way) and I cannot do fastboot.

build.prop attached. Also, here is a (mostly useless) boot log from the internal serial port (115200-8N1)

Android Bootloader - UART_DM Initialized!!!
[0] welcome to lk: current version is lk_rel_3.0.1_02272014
[10] platform_init()
[10] target_init(): platform_id 109
[10] Its BUELLER. revision 3
[70] display_init(),target_id=7337.
[70] hdmi_msm_panel_init: default format=4
[2730] splash_screen_mmc :235, 67
[2750] Config HDMI PANEL.
[2750] Turn on HDMI PANEL.
[2760] EDID: no DTD or non-DTD data present
[2760] EDID: no DTD or non-DTD data present
[2760] hdmi_edid_get_audio_data: No adb found
[2770] hdmi_audio_playback: 48KHz not supported by TV
[2770] hdmi_msm_audio_acr_setup: video format 0 not supported
[2780] aboot_init: calling idme_initialize
[2780] Idme version is 2.0 and set related function to V2.0
[2790] IDME INFO: checking for new items to add (stored items:12 specified items:12)
[2790] serial num from idme: XXXXXXXXXXXXXXXXXX
[2800] Reboot -- restart_reason=427810811 (0x197fdffb)
[2800] aboot_init: IDME - device boot up info
[2810] idme items number:12
[2810] name: board_id, size: 16, exportable: 1, permission: 292, data= XXXXXXXXXXXXXXXXXX
[2820] name: serial, size: 16, exportable: 1, permission: 292, data= XXXXXXXXXXXXXXXXXX
[2830] name: mac_addr, size: 16, exportable: 1, permission: 292, data= XXXXXXXXXXXXXXXXXX
[2830] name: bt_mac_addr, size: 16, exportable: 1, permission: 292, data= XXXXXXXXXXXXXXXXXX
[2840] name: productid, size: 32, exportable: 1, permission: 292, data= 00000000000000000000000000000000
[2850] name: productid2, size: 32, exportable: 1, permission: 292, data= 00000000000000000000000000000000
[2860] name: bootmode, size: 4, exportable: 1, permission: 292, data= 1
[2860] name: postmode, size: 4, exportable: 1, permission: 292, data= 2
[2870] name: bootcount, size: 8, exportable: 1, permission: 292, data= 32
[2880] name: eth_mac_addr, size: 16, exportable: 1, permission: 292, data= XXXXXXXXXXXXXXXXXX
[2890] bootcount = 33
[3080] aboot_init: Boot linux from MMC
[3090] boot_into_recovery=0 idme_bootmode=1 (NORMAL)
[3090] use_signed_kernel=1, is_unlocked=0, is_tampered=0.
[3100] Loading boot image (6344704): start
[3340] Loading boot image (6344704): done
[3340] Authenticating boot image (6344704): start
[3350] Attempting to enable ce3_src_clk before setting its rate.[3360] TZ channel swith returned 0
[5070] TZ channel swith returned 0
[5070] Authenticating boot image: done return value = 1
[5090] cmdline = 'androidboot.hardware=qcom user_debug=31 msm_rtb.filter=0x3F ehci-hcd.park=3 maxcpus=2'
[5100] Power on reason 1
[5100] Its bueller again 3.
[5100] cmdline_length=170, n=172, n1=45
[5110] IDME: idme atag init (export to kernel), atag_size=514
[5110] name: board_id, size: 16, exportable: 1, permission: 292, data: XXXXXXXXXXXXXXXXXX
[5120] name: serial, size: 16, exportable: 1, permission: 292, data: XXXXXXXXXXXXXXXXXX
[5130] name: mac_addr, size: 16, exportable: 1, permission: 292, data: XXXXXXXXXXXXXXXXXX
[5140] name: bt_mac_addr, size: 16, exportable: 1, permission: 292, data: XXXXXXXXXXXXXXXXXX
[5140] name: productid, size: 32, exportable: 1, permission: 292, data: 00000000000000000000000000000000
[5150] name: productid2, size: 32, exportable: 1, permission: 292, data: 00000000000000000000000000000000
[5160] name: bootmode, size: 4, exportable: 1, permission: 292, data: 1
[5170] name: postmode, size: 4, exportable: 1, permission: 292, data: 2
[5180] name: bootcount, size: 8, exportable: 1, permission: 292, data: 33
[5180] name: eth_mac_addr, size: 16, exportable: 1, permission: 292, data: XXXXXXXXXXXXXXXXXX
[5190] The atag idme items number:11

booting linux @ 0x80208000, ramdisk @ 0x82200000 (368957)