"plus" icon not showing in Finder bar

In TotalFinder, I do not see the “plus” for adding a new tab to a Finder window (only the “frame” in which the plus should be displayed - and clicking in that frame works perfectly). I see the plus in published screenshots of the program, but have never seen in on either my MBP 13" (mid 2009) nor my MBP 13" (late 2013), regardless of the OS (now 10.9.1 on both machines, but the I had the same problem since the start, when I used some version of 10.6). I have cleanly installed the app on my new (cleanly installed, too) MBP, from a fresh download. What could the problem be? It is only a cosmetic thing, but nevertheless I’d like it to work.