Hide Tabs in Firefox

useful when using [[tree style tabs]]
[[go]] https://superuser.com/questions/1424478/can-i-hide-native-tabs-at-the-top-of-firefox
- in about:config, set toolkit.legacyUserProfileCustomizations.stylesheets to true
- create userChrome.css in .mozilla/firefox//chrome (/chrome might need to be created)
- paste the following:

/* hides the native tabs */
#TabsToolbar {
  visibility: collapse;
}