Side note since you mentioned "firing". The article's title ("facing firing") may unintentionally overstate what Amazon's appeal process is actually appealing.
Based on the text, Amazon's "appeal process" is to challenge the status of being put on PIP - the Performance Improvement Plan. It isn't to appeal a firing. (Although I understand that some see that as no difference if a PIP is ~99% equivalent to getting fired eventually.)
If the employee wants to keep working (at least temporarily) for Amazon, he/she doesn't need to appeal. What a successful appeal does is let them work without PIP targets hanging over their head.