I'm using Windows 7, Firefox 29. I actually like the rounded corners part of FF29, but, as noted previously, CT 23.5 (and 23.1) breaks that feature. I had to roll back to CT 22.9 to get it to work.
I tried jwh's suggestion of commenting out the section in clrtabs, and while it did round the corners again, it also put that bar of color on either side of the tab name as shown in the first post of this thread.