>>441
後は自分でやって
https://www.reddit.com/r/FirefoxCSS/comments/116dind/how_to_hide_tab_bar_with_only_one_tab_after_1100/ */

#tabbrowser-tabs:has(.tabbrowser-tab:only-of-type) #tabs-newtab-button,
#TabsToolbar-customization-target:has(.tabbrowser-tab:only-of-type) #alltabs-button,
#tabbrowser-tabs .tabbrowser-tab:only-of-type{
visibility: collapse !important;
}