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