Firefox Client Side Decorations: close, minimize, maximize on the left

userChrome.css

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

#titlebar-max {
	-moz-box-ordinal-group: 0;
}

#titlebar-content {
	direction: rtl;
}

#TabsToolbar {
  direction: rtl;
}

#tabbrowser-tabs {
  direction: ltr;
}

.titlebar-buttonbox {
  display: flex;
}

.titlebar-min {
  order: 2;
}

.titlebar-max {
  order: 1;
}

.titlebar-close {
  order: 3;
  margin-right: 6px !important;
}