--- a/devtools/client/inspector/inspector.xhtml
+++ b/devtools/client/inspector/inspector.xhtml
@@ -9,17 +9,16 @@
   <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
 
   <link rel="stylesheet" href="chrome://devtools/skin/widgets.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/inspector.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/rules.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/computed.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/fonts.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/boxmodel.css"/>
-  <link rel="stylesheet" href="chrome://devtools/skin/deprecated-boxmodel.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/layout.css"/>
   <link rel="stylesheet" href="chrome://devtools/skin/animationinspector.css"/>
   <link rel="stylesheet" href="resource://devtools/client/shared/components/sidebar-toggle.css"/>
   <link rel="stylesheet" href="resource://devtools/client/shared/components/tabs/tabs.css"/>
   <link rel="stylesheet" href="resource://devtools/client/shared/components/tabs/tabbar.css"/>
   <link rel="stylesheet" href="resource://devtools/client/inspector/components/inspector-tab-panel.css"/>
   <link rel="stylesheet" href="resource://devtools/client/shared/components/splitter/split-box.css"/>
   <link rel="stylesheet" href="resource://devtools/client/inspector/layout/components/Accordion.css"/>

--- a/devtools/client/jar.mn
+++ b/devtools/client/jar.mn
@@ -172,17 +172,16 @@ devtools.jar:
     skin/images/item-toggle.svg (themes/images/item-toggle.svg)
     skin/images/item-arrow-dark-rtl.svg (themes/images/item-arrow-dark-rtl.svg)
     skin/images/item-arrow-dark-ltr.svg (themes/images/item-arrow-dark-ltr.svg)
     skin/images/item-arrow-rtl.svg (themes/images/item-arrow-rtl.svg)
     skin/images/item-arrow-ltr.svg (themes/images/item-arrow-ltr.svg)
     skin/images/noise.png (themes/images/noise.png)
     skin/images/dropmarker.svg (themes/images/dropmarker.svg)
     skin/boxmodel.css (themes/boxmodel.css)
-    skin/deprecated-boxmodel.css (themes/deprecated-boxmodel.css)
     skin/images/geometry-editor.svg (themes/images/geometry-editor.svg)
     skin/images/pause.svg (themes/images/pause.svg)
     skin/images/play.svg (themes/images/play.svg)
     skin/images/fast-forward.svg (themes/images/fast-forward.svg)
     skin/images/rewind.svg (themes/images/rewind.svg)
     skin/images/debugger-step-in.svg (themes/images/debugger-step-in.svg)
     skin/images/debugger-step-out.svg (themes/images/debugger-step-out.svg)
     skin/images/debugger-step-over.svg (themes/images/debugger-step-over.svg)

deleted file mode 100644
--- a/devtools/client/themes/deprecated-boxmodel.css
+++ /dev/null
@@ -1,259 +0,0 @@
-/* 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/ */
-
-/**
- * THIS STYLESHEET IS FOR THE DEPRECATED BOX MODEL MODULE (deprecated-box-model.js) AND
- * SHOULD NO LONGER BE MODIFIED.
- */
-
-#old-boxmodel-wrapper {
-  border-bottom-style: solid;
-  border-bottom-width: 1px;
-  border-color: var(--theme-splitter-color);
-  -moz-user-select: none;
-}
-
-#old-boxmodel-container {
-  /* The view will grow bigger as the window gets resized, until 400px */
-  max-width: 400px;
-  margin: 0px auto;
-  padding: 0;
-}
-
-/* Header */
-
-#old-boxmodel-header,
-#old-boxmodel-info {
-  display: flex;
-  align-items: center;
-  padding: 4px 17px;
-}
-
-#old-layout-geometry-editor {
-  visibility: hidden;
-}
-
-#old-layout-geometry-editor::before {
-  background: url(images/geometry-editor.svg) no-repeat center center / 16px 16px;
-}
-
-/* Main: contains the box-model regions */
-
-#old-boxmodel-main {
-  position: relative;
-  box-sizing: border-box;
-  /* The regions are semi-transparent, so the white background is partly
-     visible */
-  background-color: white;
-  color: var(--theme-selection-color);
-  /* Make sure there is some space between the window's edges and the regions */
-  margin: 0 14px 4px 14px;
-  width: calc(100% - 2 * 14px);
-}
-
-.old-boxmodel-margin,
-.old-boxmodel-size {
-  color: var(--theme-highlight-blue);
-}
-
-/* Regions are 3 nested elements with wide borders and outlines */
-
-#old-boxmodel-content {
-  height: 18px;
-}
-
-#old-boxmodel-margins,
-#old-boxmodel-borders,
-#old-boxmodel-padding {
-  border-color: hsla(210,100%,85%,0.2);
-  border-width: 18px;
-  border-style: solid;
-  outline: dotted 1px hsl(210,100%,85%);
-}
-
-#old-boxmodel-margins {
-  /* This opacity applies to all of the regions, since they are nested */
-  opacity: .8;
-}
-
-/* Regions colors */
-
-#old-boxmodel-margins {
-  border-color: #edff64;
-}
-
-#old-boxmodel-borders {
-  border-color: #444444;
-}
-
-#old-boxmodel-padding {
-  border-color: #6a5acd;
-}
-
-#old-boxmodel-content {
-  background-color: #87ceeb;
-}
-
-.theme-firebug #old-boxmodel-main,
-.theme-firebug #old-boxmodel-borders,
-.theme-firebug #old-boxmodel-content {
-  border-style: solid;
-}
-
-.theme-firebug #old-boxmodel-main,
-.theme-firebug #old-boxmodel-header {
-  font-family: var(--proportional-font-family);
-}
-
-.theme-firebug #old-boxmodel-main {
-  color: var(--theme-body-color);
-  font-size: var(--theme-toolbar-font-size);
-}
-
-.theme-firebug #old-boxmodel-header {
-  font-size: var(--theme-toolbar-font-size);
-}
-
-/* Editable region sizes are contained in absolutely positioned <p> */
-
-#old-boxmodel-main > p {
-  position: absolute;
-  pointer-events: none;
-  margin: 0;
-  text-align: center;
-}
-
-#old-boxmodel-main > p > span,
-#old-boxmodel-main > p > input {
-  vertical-align: middle;
-  pointer-events: auto;
-}
-
-/* Coordinates for the region sizes */
-
-.old-boxmodel-top,
-.old-boxmodel-bottom {
-  width: calc(100% - 2px);
-  text-align: center;
-}
-
-.old-boxmodel-padding.old-boxmodel-top {
-  top: 37px;
-}
-
-.old-boxmodel-padding.old-boxmodel-bottom {
-  bottom: 38px;
-}
-
-.old-boxmodel-border.old-boxmodel-top {
-  top: 19px;
-}
-
-.old-boxmodel-border.old-boxmodel-bottom {
-  bottom: 20px;
-}
-
-.old-boxmodel-margin.old-boxmodel-top {
-  top: 1px;
-}
-
-.old-boxmodel-margin.old-boxmodel-bottom {
-  bottom: 2px;
-}
-
-.old-boxmodel-size,
-.old-boxmodel-margin.old-boxmodel-left,
-.old-boxmodel-margin.old-boxmodel-right,
-.old-boxmodel-border.old-boxmodel-left,
-.old-boxmodel-border.old-boxmodel-right,
-.old-boxmodel-padding.old-boxmodel-left,
-.old-boxmodel-padding.old-boxmodel-right {
-  top: 22px;
-  line-height: 80px;
-}
-
-.old-boxmodel-size {
-  width: calc(100% - 2px);
-}
-
-.old-boxmodel-margin.old-boxmodel-right,
-.old-boxmodel-margin.old-boxmodel-left,
-.old-boxmodel-border.old-boxmodel-left,
-.old-boxmodel-border.old-boxmodel-right,
-.old-boxmodel-padding.old-boxmodel-right,
-.old-boxmodel-padding.old-boxmodel-left {
-  width: 21px;
-}
-
-.old-boxmodel-padding.old-boxmodel-left {
-  left: 35px;
-}
-
-.old-boxmodel-padding.old-boxmodel-right {
-  right: 35px;
-}
-
-.old-boxmodel-border.old-boxmodel-left {
-  left: 16px;
-}
-
-.old-boxmodel-border.old-boxmodel-right {
-  right: 17px;
-}
-
-.old-boxmodel-margin.old-boxmodel-right {
-  right: 0;
-}
-
-.old-boxmodel-margin.old-boxmodel-left {
-  left: 0;
-}
-
-.old-boxmodel-rotate.old-boxmodel-left:not(.old-boxmodel-editing) {
-  transform: rotate(-90deg);
-}
-
-.old-boxmodel-rotate.old-boxmodel-right:not(.old-boxmodel-editing) {
-  transform: rotate(90deg);
-}
-
-/* Legend: displayed inside regions */
-
-.old-boxmodel-legend {
-  position: absolute;
-  margin: 2px 6px;
-  z-index: 1;
-}
-
-.old-boxmodel-legend[data-box="margin"] {
-  color: var(--theme-highlight-blue);
-}
-
-/* Editable fields */
-
-.old-boxmodel-editable {
-  border: 1px dashed transparent;
-  -moz-user-select: none;
-}
-
-.old-boxmodel-editable:hover {
-  border-bottom-color: hsl(0, 0%, 50%);
-}
-
-/* Make sure the content size doesn't appear as editable like the other sizes */
-
-.old-boxmodel-size > span {
-  cursor: default;
-}
-
-/* Box Model Info: contains the position and size of the element */
-
-#old-boxmodel-element-size {
-  flex: 1;
-}
-
-#old-boxmodel-position-group {
-  display: flex;
-  align-items: center;
-}