There are a number of tests that assume an exact number of default widgets exist in the panel. If we add a new default button these tests break for reasons unrelated to the new widget. These tests should be refactored to handle default placements changing. The following tests have this problem and needed hacks to have the test pass after adding the sync-button to the panel by default in bug 1201331 > browser/components/customizableui/test/browser_876944_customize_mode_create_destroy.js > browser/components/customizableui/test/browser_880382_drag_wide_widgets_in_panel.js > browser/components/customizableui/test/browser_890140_orphaned_placeholders.js