from dmesg information:
visit http://wireless.kernel.org/en/usersDrivers/b43#devicefirmware
-> http://linuxwireless.sipsolutions.net/en/users/Drivers/b43/
->
https://help.ubuntu.com/community/WifiDocs/Driver/bcm43xx#b43legacy_driver_.28Open-source.29
-> download
 http://downloads.openwrt.org/sources/wl_apsta-3.130.20.0.o 
download and install
b43-fwcutter package
then:
sudo b43-fwcutter -w /lib/firmware wl_apsta-3.130.20.0.o

Firmware installed O.K.
but: b43legacy phy0 error PHY transmission error
wlan0 never worked.

Actually, it is working intermittently; ping 192.168.0. gets response intermittently.

Then from debian formal site (contrib)
https://packages.debian.org/stretch/firmware-b43legacy-installer
Download and xfer to debian; gdebi failed because of no internet connection. But seemingly, it will follows the same action above.
Files can be found: /usr/share/doc/firmware-b43legacy-installer.
Didn’t try further.