Mozilla released a standalone Firefox Nightly test build recently that includes support for vertical tabs. Here is how it looks.
  • Bit-ManEnglish
    0•3 months ago

    I’m using vertical tabs since 4 years ago and to do so installed Tree Style Tab (https://tinyurl.com/y5gr4dyn)

    Also has to disable horizontal tabs create or update the file chrome/userChrome.css located at your profile with

    #TabsToolbar {
  visibility: collapse;
}

    and add the setting toolkit.legacyUserProfileCustomizations.stylesheets with value true (use about:config)