IT reads that I have Broadcom 4306 but firmware is missing.
Plug in an ethernet cable, then use the Additional Drivers program.
You can get to the 'Additional Drivers' application by clicking on the 'Gear' at the top right. Then selecting 'System Settings'. In the window that pops up, select 'Additional Drivers' under the Hardware heading.
You can also get there by opening a terminal and entering
I'm pretty sure the Broadcom STA driver will be the one you're looking for.