Update to latest version to fix problems Rated 5 out of 5 stars
I had the same overlapping tabs bug as well (in vertical tabs) after FF updated to 14.0.1, but the problem was fixed once i updated to the latest version of Tree Style Tabs (updated to 0.14.2012081101 from current stable 0.14.2012050301).
It's recommended to check if there is a new version waiting approval (you can find them in Version Information -> See complete version history)
Superb addon Rated 5 out of 5 stars
Superb addon (expecially with wide screen monitors)
Problem: Firefox 3.5 with Metal skin has styling problems when the tab bar is located on the left or right sides