Correct horizontal alignement
Override chrome://global/skin/global.css
dialog {
  padding-top: 8px;
  padding-bottom: 10px;
  -moz-padding-start: 8px;
  -moz-padding-end: 10px;
}
(#3)
Ensure that added row is completely visible
(#3)
Simplify code to select nearest not removed item
(#3)
Don't reset options immediately, just read data from default branch
(#3)
Simplify: getOptionsHash() isn't needed anymore
(#3)