[One (M7) Original Android Development] Bastaerd:
Most of us know the feeling, but if a day had 48 hours it still would be the same. Real life is more important then devving ;)

Oh and for the people still rocking the 4.2.2 firmware, upgrading to 4.4.3 firmware without losing data and recovery is easy!

Step 1: Download the firmware here.

Step 2: [IMPORTANT] Check the MD5 hash of the file! Only go to step 3 if the hash matches or you can risk turning your phone into a brick!

Step 3: Rename the file to firmware.zip

Step 4: Reboot into your bootloader, either with power menu or with adb (adb start-server -> abd reboot-bootloader)

Step 5: Run: fastboot oem rebootRUU. You should see a silver HTC logo come up on your phone after executing this command. If this command freezes, just disconnect the USB cable and hold the power and volume down buttons until the device reboots. Then, repeat steps 4 and 5 again.

Step 6: Run: fastboot flash zip C:\location\firmware.zip. Change the location according to where you have downloaded your file. You can also move the firmware.zip into the folder where fastboot.exe is located, then the command is: fastboot flash zip firmware.zip. Output looks like this:

fastboot flash zip firmware.zip
target reported max download size of 1526722560 bytes
sending 'zip' (24923 KB)...
OKAY [ 2.430s]
writing 'zip'...
(bootloader) zip header checking...
(bootloader) zip info parsing...
(bootloader) checking model ID...
(bootloader) checking custom ID...
(bootloader) start image[hboot] unzipping for pre-update check...
(bootloader) start image[hboot] flushing...
(bootloader) [RUU]WP,hboot,0
(bootloader) [RUU]WP,hboot,99
(bootloader) [RUU]WP,hboot,100
(bootloader) ...... Successful
FAILED (remote: 90 hboot pre-update! please flush image again immediately)
finished. total time: 4.364s

Step 7: Run the command again, since 1st time always fails. It is a preparation step. After the 2nd time your output looks like this:

fastboot flash zip firmware.zip
target reported max download size of 1526722560 bytes
sending 'zip' (24923 KB)...
OKAY [ 2.431s]
writing 'zip'...
(bootloader) zip header checking...
(bootloader) zip info parsing...
(bootloader) checking model ID...
(bootloader) checking custom ID...
(bootloader) start image[radio] unzipping & flushing...
(bootloader) [RUU]UZ,radio,0
(bootloader) [RUU]UZ,radio,5
(bootloader) [RUU]UZ,radio,11
(bootloader) [RUU]UZ,radio,17
(bootloader) [RUU]UZ,radio,23
(bootloader) [RUU]UZ,radio,29
(bootloader) [RUU]UZ,radio,34
(bootloader) [RUU]UZ,radio,40
(bootloader) [RUU]UZ,radio,46
(bootloader) [RUU]UZ,radio,52
(bootloader) [RUU]UZ,radio,58
(bootloader) [RUU]UZ,radio,63
(bootloader) [RUU]UZ,radio,69
(bootloader) [RUU]UZ,radio,75
(bootloader) [RUU]UZ,radio,81
(bootloader) [RUU]UZ,radio,86
(bootloader) [RUU]UZ,radio,92
(bootloader) [RUU]UZ,radio,98
(bootloader) [RUU]UZ,radio,100
(bootloader) [RUU]WP,radio,0
(bootloader) [RUU]WP,radio,23
(bootloader) [RUU]WP,radio,46
(bootloader) [RUU]WP,radio,69
(bootloader) [RUU]WP,radio,92
(bootloader) [RUU]WP,radio,100
(bootloader) ...... Successful
OKAY [ 8.722s]
finished. total time: 11.153s

Step 8: A progress bar appears and it seems to be stuck, which is normal. Reboot your phone with: fastboot reboot, and enjoy your 4.4.3 firmware!