My goal is to add "Restore Previous Session" button to navigation bar. I can add it by modifying parameter at about:config browser.uiCustomization.state: {"placements":{"widget-overflow-fixed-list":[],"PersonalToolbar":[],"nav-bar":["back-button","forward-button","urlbar-container","stop-reload-button","search-container","customizableui-special-spring2","downloads-button","fullscreen-button","developer-button","_7a7a4a92-a2a0-41d1-9fd7-1e92480d612d_-browser-action"],"TabsToolbar":["tabbrowser-tabs","history-panelmenu","alltabs-button"],"toolbar-menubar":["menubar-items","customizableui-special-separator1","new-window-button","new-tab-button","print-button","customizableui-special-separator2","personal-bookmarks"]},"seen":["developer-button","webide-button","_7a7a4a92-a2a0-41d1-9fd7-1e92480d612d_-browser-action"],"dirtyAreaCache":["PersonalToolbar","nav-bar","TabsToolbar","toolbar-menubar"],"currentVersion":12,"newElementCount":13} The only thing I need is to know "Restore Previous Session" button name, and then add to that long line above. Is it possible?