[Feature] Hide the tab bar if there is only one tab

[gaussandhisgun]

Is your feature request related to a problem? Please describe.

Epiphany (also known as Gnome Web) hides the tab bar if there is only one tab to display. Makes perfect sense, right? If there are no tabs to switch, there should not be a switcher.

Describe the solution you'd like

Hiding the tab bar when there is only one tab in it.

Describe alternatives you've considered

This CSS:

#tabbrowser-arrowscrollbox:not(:has(.tabbrowser-tab + .tabbrowser-tab)) {
    visibility: collapse !important;
}

works for me in Firefox 117.

Additional context

[rafaelmardojai]

The theme as an optional feature for that, check the readme: https://github.com/rafaelmardojai/firefox-gnome-theme#enabling-optional-features