How to manually install WiFi firmware on Debian Live?

[Cmdte Alpha Tigre Z <santiagopinth@gmail.com>]

Hello.

I tried to make a "Realtek RTL8191SU Wireless LAN 802.11n USB 2.0
Network Adapter" work on Debian 10 Live with LXDE, but I couldn't.
Here is what I already have tried:

1-. Downloaded package firmware-realtek from package.debian.org.
2-. Booted Debian Live.
3-. Copied package from hard disk to the desktop (apt complains when
I load it directly).
4-. Executed: sudo apt install firmware-realtek
5-. Executed: sudo depmod -a
6-. Executed: sudo modprobe r8712u

Then, Wicd didn't show anything.  I ran udevadm, I don't remember how,
to see if the USB WiFi adapter was detected; it was and also
the module r8712u was loaded for it.

I need some help here, please.  I don't want to use a non-free firmware
live image.  Thanks.