Use este add on, ele permitirá colorir o DOM firefox, personalizar, adicionar muitos outros efeitos
Faça o download aqui: link
@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document url("chrome://browser/content/devtools/markup-view.xhtml") {
body { background: white !important }
}
O acima é uma amostra apenas para o fundo. Outro exemplo css é um abaixo.
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
* {
padding: 0;
margin: 0;
}
body {
color: hsl(0,0%,50%);
background: black !important;
}
.text {
color: white !important;
}
.newattr {
cursor: pointer;
}
.selected {
background-color: hsl(0,0%,90%);
}
/* Give some padding to focusable elements to match the editor input
* that will replace them. */
span[tabindex] {
display: inline-block;
padding: 1px 0;
}
li.container {
position: relative;
padding: 2px 0 0 2px;
}
.codebox {
padding-left: 14px;
}
.expander {
position: absolute;
-moz-appearance: treetwisty;
top: 0;
left: 0;
width: 14px;
height: 14px;
}
.expander[expanded] {
-moz-appearance: treetwistyopen;
}
.more-nodes {
padding-left: 16px;
}
.styleinspector-propertyeditor {
border: 1px solid #CCC;
}
}