Whatever you try, don't flash the bootloaders from any other phone to your device, unless you absolutely know what you're doing.
Originally Posted by francescopp
As the title says, can I flash a firmware from the European qualcomm S5 SM-G900F in my t mobile SM-G900T??
I want to flash the uk version SM-G900FXXU1ANCE since those from europe are mostly bloatware-free (the ones that are not from a carrier)
Otherwise, you might just give it a shot. If you have a good recovery (e.g. TWRP) or something that you can use to get back to stock easily, then there's little risk. Keep in mind that you'll only want to flash the Kernel and the ROM, but you'll want to leave everything else alone (bootloaders and recovery for example).
If by "firmware from...", you mean the odin/kies firmware package, then these typically include the whole shebang. These will probably have bootloaders, recovery, and every partition included. I don't recommend using these unless you know how to dissect them and remove the bad parts.