If you're having issues with the "Failed fetching the CDN configuration file" try this:
Download the following files: https://cdn.discordapp.com/attachments/456860411682095124/457547475969114132/config.rar https://cdn.discordapp.com/attachments/376808947992100867/463974179642015744/FS735.wtf
Extract the config.rar to Data folder
and copy FS735.wtf to WTF folder
after that remove the read only
from the world of warcraft folder
and execute either Firestorm-64.exe as admin or Firestorm Launcher as admin