/* buttons */

/* Note: Values in nsNativeTheme IsWidgetStyled function
   need to match button background/border values here */

button,
input[type="reset"],
input[type="button"],
input[type="submit"] {
  -moz-appearance: button;
  /* The sum of border-top, border-bottom, padding-top, padding-bottom
     must be the same here, for text inputs, and for <select>.  For
     buttons, make sure to include the -moz-focus-inner border/padding. */
  padding: 0px 6px 0px 6px;
  border: 2px outset ButtonFace;
  background-color: ButtonFace;
  color: ButtonText;
  font: -moz-button;
  line-height: normal !important;
  white-space: pre;
  cursor: default;
  -moz-box-sizing: border-box;
  -moz-user-select: none;
  -moz-binding: none;
  text-align: center;
}

button {
  /* Buttons should lay out like "normal" html, mostly */
  white-space: inherit;
  text-indent: 0;
}

*|*::-moz-button-content {
  display: block;
}

button:hover,
input[type="reset"]:hover,
input[type="button"]:hover,
input[type="submit"]:hover {
  background-color: -moz-buttonhoverface;
  color: -moz-buttonhovertext;
}

button:active:hover,
input[type="reset"]:active:hover,
input[type="button"]:active:hover,
input[type="submit"]:active:hover {
  padding: 0px 5px 0px 7px;
  border-style: inset;
  background-color: ButtonFace;
  color: ButtonText;
}

button::-moz-focus-inner,
input[type="reset"]::-moz-focus-inner,
input[type="button"]::-moz-focus-inner,
input[type="submit"]::-moz-focus-inner,
input[type="file"] > input[type="button"]::-moz-focus-inner {
  padding: 0px 2px 0px 2px;
  border: 1px dotted transparent;
}

button:focus::-moz-focus-inner,
input[type="reset"]:focus::-moz-focus-inner,
input[type="button"]:focus::-moz-focus-inner,
input[type="submit"]:focus::-moz-focus-inner,
input[type="file"] > input[type="button"]:focus::-moz-focus-inner {
  border-color: ButtonText;
}

button[disabled]:active, button[disabled],
input[type="reset"][disabled]:active,
input[type="reset"][disabled],
input[type="button"][disabled]:active,
input[type="button"][disabled],
select[disabled] > input[type="button"],
select[disabled] > input[type="button"]:active,
input[type="submit"][disabled]:active,
input[type="submit"][disabled] {
  /* The sum of border-top, border-bottom, padding-top, padding-bottom
     must be the same here and for text inputs */
  padding: 0px 6px 0px 6px;
  border: 2px outset ButtonFace;
  color: GrayText;
  cursor: inherit;
}

Defaults buttons back to default after button styles have been specified (except Aqua buttons on Safari).

Remove button styles

CSS