The title pretty much says it all. The tabs all look the same. There is a very narrow 3D border around the active tab in light gray. I have to stop and stare to figure out which one is active, and sometimes click a couple of tabs until I figure out which one I am on.
People have been complaining about this for 10 years though I did not notice it until recently, so maybe it’s a regression. I am on Firefox 114.