[One (M8) Q&A, Help & Troubleshooting] ckpv5:
For those who need the signed firmware, below are the Marshmallow firmware that I have :

Important : If you're flashing this Marshmallow firmware on top of a lollipop and there are two Marshmallow versions,

install the first version then follow by the second version.

Don't install directly the second version as it is only partial firmware (except fw_6.20.709.2);

without the first version is installed prior to the second version your device firmware won't be correctly updated

CID ORANG001

MID 0P6B10000

fw_6.12.61.4

CID ORANGB10

MID 0P6B10000

fw_6.14.69.4

CID ORANG309

MID 0P6B10000

fw_6.14.75.4

CID T-MOB101

MID 0P6B10000

fw_6.12.111.4

CID T-MOB102

MID 0P6B10000

fw_6.12.112.4

CID T-MOB003

MID 0P6B10000

fw_6.12.114.4

CID T-MOB009

MID 0P6B10000

fw_6.12.118.4

CID VODAP001, VODAP102, VODAPE17, VODAP405, VODAP304, VODAPD18

MID 0P6B10000

fw_6.12.161.4

CID VODAP203

MID 0P6B10000

fw_6.12.163.4

CID VODAP110 & VODAP120

MID 0P6B10000

fw_6.12.166.4

CID O2___001 & O2___102

MID 0P6B10000

fw_6.13.206.5

CID HTC__001, HTC__J15, HTC__E11, HTC__203, HTC__102, HTC__405, HTC__Y13, HTC__A07, HTC__304, HTC__032, HTC__016, HTC__M27, HTC__K18, HTC__002, HTC__A48

MID 0P6B10000

fw_6.12.401.4

CID HTC__001 & HTC__J15

MID 0P6B67000

fw_6.21.401.1 - thanks @umesh.lk

CID CWS__001

MID 0P6B12000

fw_6.20.502.5

CID T-MOB010

MID 0P6B13000

fw_6.20.531.5

CID HTC__332

MID 0P6B16000

fw_6.14.599.1

CID HTC__332

MID 0P6B16000

fw_6.17.600.3

CID ROGER001

MID 0P6B16000

fw_6.13.631.7

CID TELUS001

MID 0P6B16000

fw_6.13.661.9

CID BM___001 & SASKT001

MID 0P6B16000

fw_6.13.666.7

CID HTC__044 & HTC__059

MID 0P6B11000

fw_6.14.707.1

CID HTC__622

MID 0P6B63000

fw_6.16.708.1

CID HTC__621

MID 0P6B11000

fw_6.12.709.4

fw_6.20.709.2

CID HTC__039 & VODAP021

MID 0P6B11000

fw_6.12.710.4

fw_6.24.710.1 * install this firmware only after you have fw_6.12.710.4 already installed

CID HTC__038

MID 0P6B65000

fw_6.15.720.2

CID H3G__001, H3G__106, H3G__402, H3G__G04

MID 0P6B10000

fw_6.13.771.4

CID TELST001

MID 0P6B11000

fw_6.12.841.4

fw_6.24.841.1 * install this firmware only after you have fw_6.12.841.4 already installed

CID OPTUS001

MID 0P6B65000

fw_6.12.980.5

fw_6.24.980.1 * install this firmware only after you have fw_6.12.980.5 already installed

CID HTC__247

MID 0P6B10000

fw_6.13.1020.4

CID GLOBA001

MID 0P6B13000

fw_6.13.1500.7

CID BS_US001 & BS_US002

MID 0P6B12000 & 0P6B13000

fw_6.12.1540.4

How to install firmware :

1. You need the drivers : http://xdaforums.com/showpost.php?p=64926362&postcount=4

2. If the bootloader is UNLOCKED (for S-On device only), relock it with commands:

fastboot oem lock

fastboot reboot-bootloader

If the bootloader is LOCKED, skip the above.

3. Download the official signed fw_x.xx.xxx.x.zip

4. Put the device in bootloader/fastboot mode and connect to PC, run these commands

fastboot oem rebootRUU

fastboot flash zip fw_x.xx.xxx.x.zip

you'll see ERROR/FAILED, repeat

fastboot flash zip fw_x.xx.xxx.x.zip

fastboot reboot-bootloader

then you can proceed the next step that you need to do like installing a RUU

or fastboot reboot (to directly reboot device if you already have a working OS)

Note : unlocking bootloader will wipe your internal storage, copy your files like photos, music & etc to PC first