I tried all these crazy ideas holdind down buttons taking out battery blah blah blah!!! Took phone to repair shop they couldn't even do a master reset so they ordered me a new phone on warrenty to be here in 3 days. So I came home with phone still stuck on firmware update screen. I took my battery, sim card, and memory card out for about two hours. Whenever I put it back together, it booted right up and is working fine now. Maybe this will work for someone elsr cause all the other stuff I tried did not work. Good luck!!!

I had this issue and took my battery, sim card, and memory card out for about two hours. When I put it back together, it booted right up and is working fine now.