I´ve been having this problem for a while now. Both on Snow Leopard and in Mountain Lion. Wether I´m using Safari, Firefox or Chrome, the button for opening a new pane is often times unresponsive. Sometimes it just don´t work, and I have to click on it five to six times before it works. Same goes for the close-button on panes. The "X" if you will. Has anyone else experienced this?