@rorie: Yeah, I'm on Firefox 23.0.1 as well. It looks like the flickering is specific to lower resolution browsers, which lead to the tooltip being displayed in two lines of text instead of one.
On my low resolution laptop, the tooltip hits the right side of the browser and breaks off into a second line (See "Before" image below). This allowed the cursor to overlap with the tooltip and caused the flickering.
Shifting the right panel to the left solved the problem, since the tooltip text was contained in one line (see "After shifting secondary-contents" ).