diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 7e53d402796..2b17c9e0709 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -642,6 +642,10 @@ function BrowserStartup()
       // On X, we're not currently able to account for the size of the window
       // border.  Use 28px as a guess (titlebar + bottom window border)
       defaultHeight -= 28;
+#endif
+#ifdef XP_MACOSX
+      // account for the Mac OS X title bar
+      defaultHeight -= 22;
 #endif
     }
     document.documentElement.setAttribute("width", defaultWidth);