Comment 77 for bug 950295

Probably the easiest way to test is to temporarily move the /lib/firmware/b43 directory to another location, then run 'sudo modprobe -r b43; sudo modprobe b43'. When your done you can move the directory back to its original location.

Another way would be to remove linux-firmware-nonfree before running the modprobe commands. The disadvantage of this is that you may need to use a wired connection to reinstall the package.