It's not ideal because it only works when firefox is running, but it's good, maybe someone else can perfect it. Click image to enlarge. Facebook feed is on the top left.
Using GeekTool and the Facebook Toolbar 1.4.3 for Firefox I was able to get the live feed from Facebook to show up on my desktop and look nice. Here are steps:
1) Download and install the Facebook Toolbar - in the tools menu select add ons -> Facebook toolbar -> preferences -> use built-in firefox notifications
2) Download and install GeekTool
3) Download and install Growl
4) Enable Growl's text file logging by entering these shell commands
defaults write com.Growl.GrowlHelperApp GrowlLoggingEnabled -bool YES
defaults write com.Growl.GrowlHelperApp GrowlLogType 1
defaults write com.Growl.GrowlHelperApp "Custom log history 1" ~/Library/Logs/Growl.log
5) Make a new shell geeklet and paste this code
tail -200 ~/Library/Logs/Growl.log | sed -e 's/..- Priority 0//g' -e 's/^............//g' | grep Firefox | sed 's/Firefox: Facebook Notification (//g' | tail -n 17 | grep -vw 'registered' | grep -vw 'finished downloading'
6) In the Growl Preferences you can tell it to hide growls from firefox if you don't want a growl bubble popping up anymore, don't worry it will still show up in the log.
That should do it. Enjoy.