gecko/toolkit/content/textbox.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* set default namespace to XUL */
@namespace html url("http://www.w3.org/1999/xhtml"); /* namespace for HTML elements */

html|*.textbox-input {
  -moz-appearance: none !important;
  text-align: inherit;
  text-shadow: inherit;
  -moz-box-sizing: border-box;
}

html|*.textbox-textarea {
  -moz-appearance: none !important;
  text-shadow: inherit;
  -moz-box-sizing: border-box;
}

textbox[isempty="true"] html|*.textbox-input ,
textbox[isempty="true"] html|*.textbox-textarea {
  text-align: left;
  direction: ltr;
}

textbox[isempty="true"]:-moz-locale-dir(rtl) html|*.textbox-input ,
textbox[isempty="true"]:-moz-locale-dir(rtl) html|*.textbox-textarea {
  text-align: right;
  direction: rtl;
}

textbox[isempty="true"] html|*.textbox-input[emptytextdelay="true"] ,
textbox[isempty="true"] html|*.textbox-textarea[emptytextdelay="true"] {
  color: transparent !important;
}