I found the post by jld63 the most useful, particularly where it advises in step 5 to click "NO" when asked about "setting up wireless", which is totaly counterintuitive, because setting up the wireless is the whole intention. The next steps allow you to do it. But I had to do a few other steps to make it all work:
(1) I had to restart my machine and the printer for the printer to become visible in the setup wizard (2) I had to "add" the printer in the systems prefs box, and delete the older listing of the very same printer. I think it hangs onto its old settings, but when you add it again new, it comes in with new settings. I copy here jld63's steps:
"The user manual is horribly confusing, to say the least, when it comes to setting up the wireless networking (at least to me). I suggest you ignore everything in the manual regarding networking. Let me give you Mac users some hints so you can avoid the wasted time and frustration I experienced:
1. After you've unpacked the printer, installed the toner and paper and printed a test page, go to the Apple web site and search for Brother printer drivers. Apple has all the latest drivers for download free.
2. Download and install the drivers.
3. Insert the CD that came with the printer and open the 'Utilities' folder. Do NOT use the 'Start Here OSX' icon.
4. In the Utilities folder, click on 'Wireless Device Setup Wizard.'
5. In the next window, Setting Up Wireless, click 'NO' then 'Next.'
6. In the next window, click 'checked and confirmed' then 'Next' (you don't need to read the stuff in that box).
7. In the next window, make sure 'Temporarily use USB cable' is selected, then click 'Next.'
8. Connect a USB cable from your computer to the printer.
9. In the next window, you will see the setup software searching for wireless signals in your area. Make sure your network is visible, then select it.
10. In the next window, input your router's wireless access password twice as requested. (Note: if you have an Apple Airport, do not enter the Airport PW, but your wireless access PW. If they are the same, no worries.)
11. Unplug the USB cable to the printer.
12. Click through to 'finish' and you are done!"