You can use View > Sidebar > Bookmarks (Ctrl+B) to open the bookmarks in the sidebar.

Press F10 or press and hold the Alt key down to bring up the "Menu Bar" temporarily.

Firefox 4 has two bookmark icons in the Customize window. One has a drop marker that open a Bookmark menu. The other without the drop marker is the one that opens the bookmarks in the sidebar.

Open the Customize window via "View > Toolbars > Customize" or via "Firefox > Options > Toolbar Layout"

http://kb.mozillazine.org/Toolbar_customization

Press Ctrl+B ... or open the old-style Firefox menu by pressing the Alt key, then click on View -> Sidebar -> Bookmarks

On a Mac it is Command-B.

Thanks. got it working