I think this is a problem with Safari's Full Screen mode: It sometimes, inconsistently, does not switch off its menu-hiding and dock-hiding algorithms when it is not in full-screen mode. (And I am not running Spicerack 🙂).
Quit and Relaunch Safari is a workaround, but now I cannot reproduce this hiccup. I am running Safari 6.0.2 and OS X 10.8.2 on my retina display 15" MBP. Here is what seems to be happening with this "glitch".
• Safari is active (i.e., is the foreground App) but not in full-screen mode - Safari's selected (in Safari > View > ....) Toolbar(s) and scrollbars are visible (System Preferences > General > Show Scroll bars > [Always].
• Safari's Menu Bar is hidden.
• The Dock is also hidden.
To emphasize - when not in full screen mode - Safari's Menu Bar and the Finder's Dock are hidden. I can reveal the Safari Menu Bar by moving the cursor's hot-spot (i.e., the tip of the arrow) to any point on the top edge of the display - this causes the Safari Menu Bar to drop down and become active again; also the Dock icons reappear (at the bottom of the display); and when I move the cursor away from the top of the screen, the menu bar and Dock become hidden again.
I note that this appears to be normal behaviour in Safari's "full screen mode". Except that, in full screen mode, the Dock remains hidden when the Menu Bar is revealed as described above. IMO this is a bug.