Sync to trunk.

resources/default_tweaks.py

@@ -350,3 +350,11 @@ send_news_to_device_location = "main"
 # work on all operating systems)
 server_listen_on = '0.0.0.0'
 
+#: Unified toolbar on OS X
+# If you enable this option and restart calibre, the toolbar will be 'unified'
+# with the titlebar as is normal for OS X applications. However, doing this has
+# various bugs, for instance the minimum width of the toolbar becomes twice
+# what it should be and it causes other random bugs on some systems, so turn it
+# on at your own risk!
+unified_title_toolbar_on_osx = False
+

src/calibre/gui2/layout.py

@@ -17,6 +17,7 @@ from calibre.gui2.search_box import SearchBox2, SavedSearchBox
 from calibre.gui2.throbber import ThrobbingButton
 from calibre.gui2.bars import BarsManager
 from calibre.gui2.widgets import ComboBoxWithHelp
+from calibre.utils.config_base import tweaks
 from calibre import human_readable
 
 class LocationManager(QObject): # {{{
@@ -264,6 +265,9 @@ class MainWindowMixin(object): # {{{
         for bar in self.bars_manager.child_bars:
             self.addToolBar(Qt.BottomToolBarArea, bar)
         self.bars_manager.update_bars()
+        # This is disabled because it introduces various toolbar related bugs
+        # The width of the toolbar becomes the sum of both toolbars
+        if tweaks['unified_title_toolbar_on_osx']:
             self.setUnifiedTitleAndToolBarOnMac(True)
 
         l = self.centralwidget.layout()