userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

.searchbar-search-button[addengines=true]::after,
.searchbar-search-button[addengines=true] > .searchbar-search-icon-overlay {
  visibility: hidden !important;
}

hbox.titlebar-spacer,
hbox.titlebar-buttonbox-container,
#protections-popup-settings-button,
#protections-popup-mainView-panel-header,
menuitem.customize-context-reportExtension,
menuitem.customize-context-removeExtension,
#BMB_bookmarksToolbar,
#BMB_bookmarksShowAllTop,
#BMB_viewBookmarksSidebar,
.tab-close-button,
#toolbar-context-selectAllTabs,
#toolbar-context-reloadSelectedTab,
#toolbar-context-menu > menuseparator,
.search-go-button,
#placesContext_new\:bookmark,
#placesContext_new\:separator,
#placesContext_open\:newwindow,
#placesContext_open\:newprivatewindow,
.searchbar-clear-history,
#context_closeTab,
#context_reloadTab,
#context_duplicateTab,
#context_toggleMuteTab,
#context_moveTabOptions,
#context_closeOtherTabs,
#context_closeTabsToTheEnd,
#context-back,
#context-reload,
#context-forward,
#context-inspect,
#context-savepage,
#context-viewinfo,
#context-openlink,
#context-viewsource,
#context-viewbgimage,
#context-bookmarkpage,
#context-bookmarklink,
#context-sep-viewsource,
#context-sep-navigation,
#context-sep-viewbgimage,
#context-openlinkprivate,
.urlbar-history-dropmarker,
#star-button,
#back-button,
#forward-button,
#pageActionButton,
#inspect-separator,
#statuspanel-label,
#PanelUI-menu-button,
#toggle_PersonalToolbar,
#viewToolbarsMenuSeparator,
#overflowMenu-customize-button,
#tabContextMenu > menuseparator,
.customize-context-removeFromToolbar,
#menu_openHelp,
#menu_openTour,
#menu_pageInfo,
#menu_viewPopup,
#menu_EditPopup,
#menu_FilePopup,
#menu_openDownloads,
#menu_keyboardShortcuts,
#menu_HelpPopup_reportPhishingtoolmenu,
#feedbackPage,
#helpSafeMode,
#sanitizeItem,
#webDeveloperMenu,
#devToolsSeparator,
#bookmarksMenuPopup
{display: none !important;}