Header display fixes

Hi there, sorry for the late reply to your AMO mail. Take this instead.
First of all, yep, the screenshot was taken on OSX.

I got a bit intrigued after looking for an "easy" solution.
Turns out the important bits can be found in the `.emailStar` class, namely max-width/-height: 1em and so forth.

However, what bugged me without noticing at first was also that the labels aren't aligned, as your original hbox didn't went into the grid.

This pull fixes the warning icon stuff as well as grid placement/alignment.
I tested this on OSX and a bit on Win7 with proper results. However, I cannot guarantee that I messed up some stuff. ;)

Of course, taking my code is in no way a requirement to pass a AMO review. Just trying to be helpful here....