The new layout has a bug in the "tab bar" on Firefox 36/Mac. Note the small bumps in the horizontal line. They don't appear on Safari or Chrome. ![enter image description here][1] On a fresh profile without any modificatons at all, it looks a bit different, but this changes when zooming in/out: ![enter image description here][2] I just noticed the effect can also appear when zooming on Safari and Chrome. [1]: https://i.sstatic.net/fmMLh.png [2]: https://i.sstatic.net/tJDh4.png