Custom css

gistfile1.txt

You can already do mostly what you want using a little bit of custom CSS.
On the options page -> Popup Menu -> Advanced Settings -> Customize. 
Append the following to the end of the text area: 


/* This will center the popup above the selection: */
.popup.mainmenu{ 
  transform: translate(-50%, calc(-100% - 15px));
}

/* This will break the search engines into multiple rows: */
.popup{ 
  width: 150px;
}
.popup li{
  float: left;
}

You can tweak the % and px values to fit your liking. For example the 150px value determines how many 
icons that will fit on a single line before creating new rows. 

These tweaks may break the preview of the menu on the options page, but should work real pages. 

I'm working on a new options page that should make some of these tweaks easier to do, without having to learn css.