Hello, its my first time posting here, I usually lurk but I'm having problems with the Firemoth official plug-in, namely I can open the last door to fight the boss, I get an error message about some missing skeletal animations or something. The only Mods/Plug-ins I have is the master index. any help would be greatly appreciated.

Little late here but could you post your modlist (from the bottom of your morrowind.ini) and the contents of your warnings.txt file (same place as morrowind.ini)

If you are using Liztail's Animation kit, you may also want to run the fix anim errors option there and see if that fixes it for you.