Tabs in browsers always used to be delineated, usually looking like tabs in a file cabinet. In Windows 10, running Firefox, when I open multiple tabs the delineation is not great and it just looks like random text at the top of the window, rather than clearly marked individual tabs. I've played around with Windows 10 themes/colors and with Firefox settings but can't find it.
Just another thing that the tech billionaires change on us without our consent when we update, rather than giving us the choice to change. We really need better billionaires in charge of such things.