Where can I download iOS 8.x firmware / IPSW files for the iPhone 4s?
The iPhone 4s is capable of running a limited version of the iOS 8 update. While some features are disabled on the older hardware, Apple has included performance enhancements for the 4s in version 8.1.1. Here are links to official IPSW files for the iPhone 4s.
iPhone 4s iOS 8.1.1: iPhone4,1_8.1.1_12B435_Restore.ipsw
iPhone 4s iOS 8.1.0: iPhone4,1_8.1_12B411_Restore.ipsw
iPhone 4s iOS 8.0.2: iPhone4,1_8.0.2_12A405_Restore.ipsw
iPhone 4s iOS 8.0.1: iPhone4,1_8.0.1_12A402_Restore.ipsw
iPhone 4s iOS 8.0.0: iPhone4,1_8.0_12A365_Restore.ipsw