See: http://jsfiddle.net/W5TVx/1/ In FF16.0.2 and FF 17.0.1 there are some lines faulty rendered, the descender of "g" and "y" are visually cut off. It seems that the line is rendered with 18 px height (manually calculation would result in 17px) whereas the parent receives 17px height. Even when tweaking the line heihgt little (e.g. 1.22) there seemed to be some pattern inside. I discussed that topic on the firefox IRC channel, we tested if a clean profile would fix it -- it does not but the pattern of faulty lines changes, some prefixed faulty lines were added before it started. Safari and IE9 share this problem.