I agree! The rounded corners on active (and mouseover) tabs that we get in FF without CT enabled is really nice and really helps when you have a lot of tabs open and want to see at a glance which one is the active one. It showed through a couple of releases ago, but then disappeared again. I even downgraded to version 23.8 just so I could have the rounded corners AND the CT colours on the tabs, even though I know it's not actually a good idea to use an old version.