1. about:config

2. toolkit.legacyUserProfileCustomizations.stylesheets = true

3. about:support

4. open profile folder

5. create file 'chrome/userChrome.css'

#pageActionSeparator {
 display: none !important;
}
 
#page-action-buttons #pageActionButton {
 width: 0 !important;
 padding: 0px !important;
 transition: all 1s ease-in-out;
}
 
#page-action-buttons:hover #pageActionButton {
 width: 0px !important;
 padding: 0px !important;
 transition: all 1s ease-in-out 2s;
}

#urlbar-zoom-button  { 
display: none !important; 
}

.urlbar-history-dropmarker {
  float: right  !important;
}

#reader-mode-button, #readinglist-addremove-button {
 display:none !important;
}

/* Move hamburger menu to the left */
#PanelUI-button,
#customization-panel-container,
#customization-panelWrapper .panel-arrow { 
   display:none !important;
}

/* more tools... */
#nav-bar-overflow-button {
    display: none !important;
}

.urlbar-history-dropmarker {
display: none !important;
}