Hide Firefox Tab Bar on Windows

README.md

1. Go to Menu → Help → More troubleshooting information → Application Basics → Profile Folder → Open Folder
2. Create a folder named chrome
3. Create a new text file inside chrome named userChrome.css and paste the content
4. Go to about:config in Firefox
5. Change the setting toolkit.legacyUserProfileCustomizations.stylesheets to true
6. Restart Firefox

userChrome.css

#titlebar {
    visibility: collapse;
}

#TabsToolbar .titlebar-buttonbox-container {
    visibility: visible;
    display: block;
    position: absolute;
    top: 2px;
    right: 0;
}

#nav-bar {
    padding-right: 160px;
    background-color: black !important;
}

#main-window {
    border-top: 1px solid #282828;
}