Full backup of only firmware and ROM from non-rooted Android devices (namely Samsung devices) So, I've been looking around the Web, but haven't found anything conclusive. The closest things I could find were either options after rooting or an XDA post regarding near-full backups via ADB, but nothing regarding ROM/Firmware backup only without root. My question is: "How to back up ROM/Firmware onto a PC from a non-rooted Android device (Galaxy S4 to be exact)?".
Thank you kindly in advance!
So, after the discussion in the comments you can backup the phone using the command adb backup [-f &lt;file&gt;] -all to backup all of your data, where file is you should put a recognizable name for the back up to track it easier when you will need it. Store it somewhere safe.

If you will ever need that you can use the command adb restore *name of the backup* after the flashing of the stock firmware and all will be as you wanted it.

There is more: in the case you don't want to backup ALL data, you can leave the -all option and use specific selections: 

-obb/-noobb: you can save the OBB data of every application

-apk/-noapk: you can save the application themselves

-shared/-noshared: you can do a backup of the SDCARD contents

-system/-nosystem: backup of system apps (stock ones)