Tree Tab Style without header and native tab bar

userChrome.css

.tabbrowser-tab {
  visibility: collapse;
}
#navigator-toolbox {
  background-color: #2b2a33 !important;
}
.titlebar-button {
  height: 32px !important;
}
#nav-bar {
  margin-top: -37px;
  margin-right: 140px;
  box-shadow: none !important;
}

[uidensity="compact"]:root .titlebar-button {
  height: 37px !important;
}
[uidensity="compact"]:root #nav-bar {
  margin-top: -27px;
}

.titlebar-spacer {
  background-color: var(--chrome-secondary-background-color);
}
.titlebar-buttonbox-container {
  margin-top: 3px !important;
  background-color: var(--chrome-secondary-background-color);
}
.titlebar-color {
  background-color: var(--toolbar-bgcolor);
}

#main-window[inFullscreen="true"] #sidebar-box,
#main-window[inFullscreen="true"] #sidebar-box + splitter {
    visibility: collapse;
}

#sidebar-box #sidebar-header {
  display: none !important;
}