The default bookmarks you see in Firefox release channel, are also the same for Nightly as well, but these have been changed by Mozilla recently for the latter. If you’re already using Nightly, you won’t notice the change even though you’re using the latest build, you should either create a new profile or become a new Nightly user for that. After that, when you click on the bookmarks menu icon, in the drop down, under Recently bookmarked, you’ll notice the some of the new default bookmarks.
Firefox Nightly new default bookmarks
You can find the complete set in Firefox Nightly Resources menu, here are they: Firefox Nightly blog, Mozilla bug Tracker, Mozilla developer Network, Nightly Tester tools, All your crashes, Discuss Nightly on IRC and Planet Mozilla.
Mozilla is doing all the necessary to make their bleeding edge Nightly more interesting to testers or advanced users. They’ve started a Nightly blog, created a what’s new page for Nightly and now the new default bookmarks.