In this case, a picture's worth a thousand words.
EFI is the new BIOS in case anyone who comes across this didn't know. From a separate question it was determined that driver level questions were on topic, which sits under the operating system and (arguably) next to the BIOS, so by definition BIOS level questions would have to be on topic. User space apps would not be on topic, unless they're written in assembly (!).
As far as separating the two topics, assuming you're referring to tags, I say yes. I say this because (personally) when I think of a BIOS, taking an embedded device such as a soekris box as a great example, it has a BIOS, which allows you to set options such as com port bitrate and parity, and other options like boot to network, etc.
Now, firmware is something a little different, User.1 pointed out that it's loaded onto the device and is rarely if ever changed by UI (sometimes, think internet firmware updates). I like to refer to it as 'extremely embedded', but a common term is 'deeply embedded'. However, this becomes essential when you look at how a BIOS might interact with a subsystem that's controlled by firmware, a hard drive is a perfect example, as a BIOS would communicate to the firmware and not the platters themselves to find out space, speed, and all the gushy details that makes people rush out to stores and.... I'm sure you get the point.
The moral is sometimes the BIOS and firmware are mushed together, but a lot of the time they aren't. They deserve their own tags, and in questions where both tags are warranted, it shall be sanctioned and implemented by whomever takes the initiative. :D