As always it works perfectly. Thanks a lot!

deleted by creator

Perfect!

Now it works!

I used this code:

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/tabs_on_bottom.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* IMPORTANT
Get window_control_placeholder_support.css
Window controls will be all wrong without it.
Additionally on Linux, you may need to get:
linux_gtk_window_control_patch.css

Use tabs_on_bottom_menubar_on_top_patch.css if you
have menubar permanently enabled and want it on top 
*/

#toolbar-menubar[autohide="true"] > .titlebar-buttonbox-container,
#TabsToolbar > .titlebar-buttonbox-container{
  position: fixed;
  display: block;
  top: 0px;
  right:0;
  height: 40px;
}
@media (-moz-bool-pref: "userchrome.force-window-controls-on-left.enabled"),
       (-moz-gtk-csd-reversed-placement),
       (-moz-platform: macos){
  .titlebar-buttonbox-container{ left:0; right: unset !important; }
}

:root[uidensity="compact"] #TabsToolbar > .titlebar-buttonbox-container{ height: 32px }

#toolbar-menubar[inactive] > .titlebar-buttonbox-container{ opacity: 0 }

.titlebar-buttonbox-container > .titlebar-buttonbox{ height: 100%; }

#titlebar{
  order: 2;
  -moz-appearance: none !important;
  --tabs-navbar-shadow-size: 0px;
  --uc-menubar-vertical-overlap: 19px; /* for hide_tabs_with_one_tab_w_window_controls.css compatibility */
}
/* Re-order window and tab notification boxes */
#navigator-toolbox > div{ display: contents }
.global-notificationbox,
#tab-notification-deck{
  order: 2;
}

#TabsToolbar .titlebar-spacer{ display: none; }
/* Also hide the toolbox bottom border which isn't at bottom with this setup */
#navigator-toolbox::after{ display: none !important; }

@media (-moz-gtk-csd-close-button){
  .titlebar-button{
    flex-direction: column;
  }
}

/* At Activated Menubar */
:root:not([chromehidden~="menubar"], [sizemode="fullscreen"]) #toolbar-menubar:not([autohide="true"]) + #TabsToolbar > .titlebar-buttonbox-container {
  display: block !important;
}
#toolbar-menubar:not([autohide="true"]) > .titlebar-buttonbox-container {
  visibility: hidden;
}

/* These exist only for compatibility with autohide-tabstoolbar.css */
toolbox#navigator-toolbox > toolbar#nav-bar.browser-toolbar{ animation: none; }
#navigator-toolbox:hover #TabsToolbar{ animation: slidein ease-out 48ms 1 }
#TabsToolbar > .titlebar-buttonbox-container{ visibility: visible }
:root:not([lwtheme]) #navigator-toolbox{ background-color: -moz-dialog }

/* Uncomment the following if you want bookmarks toolbar to be below tabs */
/*
#PersonalToolbar{
  order: 2;
}
*/

I think its one that you created actually

Perfect!

Thank you so much!

Perfect!

Thanks a lot!!

I see, this is for the highlighting, right?

And for the popup it would be the same? The other popups in my toolbox do look like they are intended to, its just that one that doesn’t work.