I meant to post this the other week but forgot, but a clean install has just prompted me to add it again. Found via Digital Minute

1. Click on the Bookmarks menu and select Manage Bookmarks&
2. Click the New Bookmark toolbar button
3. Enter JavaScript Console as the name
4. Enter chrome://global/content/console.xul as the location
5. Check the Load this bookmark in the sidebar checkbox
6. Click OK

Digital Media also have an updated post about styling the console.