[AT&T Samsung Galaxy S 5] samccfl99:
There is really not much more to say. It works for all of us and it is all in post #1. Pretty much what ParkerJ explained in detail. This does work! Below is what you need from the OP:

For those of you that want to have safestrap also you can easily set it up to run beside FF. Added an NG3 Flasher for the G870A. I will also provide links to the odin tars for the kernels for the G900A just in case you softbrick and need them to recover. If this is the case don't fear all you have to do is flash the NG3 Kernel in download mode through odin and reboot then enter SS through the splash.

G900A

Be on 5.0 then continue (if you're on my rom already you don't need to install busybox)

Download and install busybox from the playstore.

Install it then safestrap.

Install recovery in safestrap. It was probably removed if you used flashfire. If not you can skip this as its probably installed.

Download and install NCE Flasher (Thanks k-alz benwaffle and carl1961)

Download this Flashable OC4 Kernel zip (this one is fixed to work)

Load NCE Flasher and follow the instructions in the app which will flash the NCE Kernel for you and you'll be rebooted into SafeStrap

Flash the ROM, zips, restore your backup.

Remember to flash the OC4 Kernel back afterward or you'll be back into SS quick to do so.

Reboot

Now in case of problems download the NG3 Kernel tar and OC4 to use in odin. I chose NG3 for no particular reason. The NCE Flasher app uses NCE but all of the kernels before OC4 work for this step. The only times I find this is needed since finding the above method is when I hit a bootloop or some reason I can't get to the NCE flasher because of errors I created. Keep these kernels handy because you may run into a need to use them and unbrick.

All you'll need to do is boot to download mode and flash the NG3 kernel in odin

Odin in case you need it: https://www.androidfilehost.com/?fid=23622183712465432

G900A_NG3_Stock_Kernel.tar.md5

G900A_OC4_Stock_Kernel.tar.md5

G870A

Be on 5.0 with root (stock, anything else). Guide here: http://xdaforums.com/att-galaxy-s5/general/how-to-update-to-g870aoc5-5-0-keeproot-t3083841

Download busybox from the playstore.

Install it then safestrap. https://www.androidfilehost.com/?fid=95832962473398954

Install recovery in safestrap. It was probably removed if you used flashfire. If not you can skip this as its probably installed.

Download and install G870A NG3 Flasher (Thanks benwaffle and carl1961. I modified this to use the NG3 Kernel for you guys)

Download this Flashable OC5 Kernel zip

Load NG3 Flasher and follow the instructions in the app which will flash the NG3 Kernel for you and you'll be rebooted into SafeStrap

Flash the ROM, zips, restore your backup.

Remember to flash the OC5 Kernel back afterward or you'll be back into SS again.

Reboot

Now in case of problems download the NG3 and OC5 Kernel tars to use in odin. The only times I find this is needed since finding the above method is when I hit a bootloop or some reason and I can't get to the NG3 flasher because of errors I created. Keep these kernels handy because you may run into a need to use them and unbrick.

All you'll need to do is boot to download mode and flash the NG3 kernel in odin

G870A NG3 Kernel: https://www.androidfilehost.com/?fid=23622183712466972

G870A OC5 kernel: https://www.androidfilehost.com/?fid=95916177934556234