--- a/devtools/client/debugger/new/debugger.css
+++ b/devtools/client/debugger/new/debugger.css
@@ -321,28 +321,16 @@ menuseparator {
   --object-color: var(--theme-body-color);
   --caption-color: var(--theme-highlight-blue);
   --location-color: var(--theme-content-color1);
   --source-link-color: var(--theme-highlight-blue);
   --node-color: var(--theme-highlight-bluegrey);
   --reference-color: var(--theme-highlight-purple);
 }
 
-.theme-firebug {
-  --number-color: #000088;
-  --string-color: #ff0000;
-  --null-color: #787878;
-  --object-color: DarkGreen;
-  --caption-color: #444444;
-  --location-color: #555555;
-  --source-link-color: blue;
-  --node-color: rgb(0, 0, 136);
-  --reference-color: rgb(102, 102, 255);
-}
-
 /******************************************************************************/
 
 .objectLink:hover {
   text-decoration: underline;
 }
 
 .inline {
   display: inline;
@@ -1919,28 +1907,16 @@ html .toggle-button.end.vertical svg {
   --location-color: var(--theme-comment);
   --source-link-color: var(--theme-highlight-blue);
   --node-color: var(--theme-highlight-purple);
   --reference-color: var(--theme-highlight-blue);
   --comment-node-color: var(--theme-comment);
   --stack-function-color: var(--theme-highlight-red);
 }
 
-.theme-firebug {
-  --number-color: #000088;
-  --string-color: #FF0000;
-  --null-color: #787878;
-  --object-color: DarkGreen;
-  --caption-color: #444444;
-  --location-color: #555555;
-  --source-link-color: blue;
-  --node-color: rgb(0, 0, 136);
-  --reference-color: rgb(102, 102, 255);
-}
-
 /******************************************************************************/
 
 .inline {
   display: inline;
   white-space: normal;
 }
 
 .objectBox-object {

--- a/devtools/client/definitions.js
+++ b/devtools/client/definitions.js
@@ -496,28 +496,19 @@ Tools.darkTheme = {
 Tools.lightTheme = {
   id: "light",
   label: l10n("options.lightTheme.label2"),
   ordinal: 2,
   stylesheets: ["chrome://devtools/skin/light-theme.css"],
   classList: ["theme-light"],
 };
 
-Tools.firebugTheme = {
-  id: "firebug",
-  label: l10n("options.firebugTheme.label2"),
-  ordinal: 3,
-  stylesheets: ["chrome://devtools/skin/firebug-theme.css"],
-  classList: ["theme-light", "theme-firebug"],
-};
-
 exports.defaultThemes = [
   Tools.darkTheme,
   Tools.lightTheme,
-  Tools.firebugTheme,
 ];
 
 // White-list buttons that can be toggled to prevent adding prefs for
 // addons that have manually inserted toolbarbuttons into DOM.
 // (By default, supported target is only local tab)
 exports.ToolboxButtons = [
   { id: "command-button-splitconsole",
     description: l10n("toolbox.buttons.splitconsole", "Esc"),

--- a/devtools/client/dom/content/dom-view.css
+++ b/devtools/client/dom/content/dom-view.css
@@ -37,17 +37,17 @@ body {
 
 .treeTable .treeLabel,
 .treeTable td.treeValueCell .objectBox {
   direction: ltr; /* Don't change the direction of english labels */
 }
 
 /* Read only properties have a padlock icon */
 .treeTable tr:not(.writable) td.treeValueCell {
-  background: url("chrome://devtools/skin/images/firebug/read-only.svg") no-repeat;
+  background: url("chrome://devtools/skin/images/read-only.svg") no-repeat;
   background-position: 1px 5px;
   background-size: 10px 10px;
 }
 
 .treeTable tr:not(.writable) td.treeValueCell:dir(rtl) {
   background-position-x: right 1px;
 }
 

--- a/devtools/client/framework/test/browser_toolbox_theme.js
+++ b/devtools/client/framework/test/browser_toolbox_theme.js
@@ -19,14 +19,14 @@ add_task(function* testDevtoolsTheme() {
     "The element has an attribute based on devtools theme.");
 
   Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "dark");
   is(document.getElementById("browser-bottombox").getAttribute("devtoolstheme"), "dark",
     "The element has an attribute based on devtools theme.");
   is(document.getElementById("appcontent").getAttribute("devtoolstheme"), "dark",
     "The element has an attribute based on devtools theme.");
 
-  Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "firebug");
+  Services.prefs.setCharPref(PREF_DEVTOOLS_THEME, "unknown");
   is(document.getElementById("browser-bottombox").getAttribute("devtoolstheme"), "light",
     "The element has 'light' as a default for the devtoolstheme attribute.");
   is(document.getElementById("appcontent").getAttribute("devtoolstheme"), "light",
     "The element has 'light' as a default for the devtoolstheme attribute.");
 });

--- a/devtools/client/jar.mn
+++ b/devtools/client/jar.mn
@@ -107,17 +107,16 @@ devtools.jar:
     content/dom/dom.html (dom/dom.html)
     content/dom/main.js (dom/main.js)
     content/accessibility/accessibility.html (accessibility/accessibility.html)
     content/accessibility/main.js (accessibility/main.js)
 %   skin devtools classic/1.0 %skin/
     skin/devtools-browser.css (themes/devtools-browser.css)
     skin/dark-theme.css (themes/dark-theme.css)
     skin/light-theme.css (themes/light-theme.css)
-    skin/firebug-theme.css (themes/firebug-theme.css)
     skin/toolbars.css (themes/toolbars.css)
     skin/toolbox.css (themes/toolbox.css)
     skin/tooltips.css (themes/tooltips.css)
     skin/images/accessibility.svg (themes/images/accessibility.svg)
     skin/images/add.svg (themes/images/add.svg)
     skin/images/breadcrumbs-divider.svg (themes/images/breadcrumbs-divider.svg)
     skin/images/filters.svg (themes/images/filters.svg)
     skin/images/filter-swatch.svg (themes/images/filter-swatch.svg)
@@ -264,54 +263,17 @@ devtools.jar:
     skin/images/security-state-insecure.svg (themes/images/security-state-insecure.svg)
     skin/images/security-state-secure.svg (themes/images/security-state-secure.svg)
     skin/images/security-state-weak.svg (themes/images/security-state-weak.svg)
     skin/images/diff.svg (themes/images/diff.svg)
     skin/images/import.svg (themes/images/import.svg)
     skin/images/pane-collapse.svg (themes/images/pane-collapse.svg)
     skin/images/pane-expand.svg (themes/images/pane-expand.svg)
     skin/images/help.svg (themes/images/help.svg)
-
-    # Firebug Theme
-    skin/images/firebug/read-only.svg (themes/images/firebug/read-only.svg)
-    skin/images/firebug/twisty-closed-firebug.svg (themes/images/firebug/twisty-closed-firebug.svg)
-    skin/images/firebug/twisty-open-firebug.svg (themes/images/firebug/twisty-open-firebug.svg)
-    skin/images/firebug/arrow-down.svg (themes/images/firebug/arrow-down.svg)
-    skin/images/firebug/arrow-up.svg (themes/images/firebug/arrow-up.svg)
-    skin/images/firebug/close.svg (themes/images/firebug/close.svg)
-    skin/images/firebug/pause.svg (themes/images/firebug/pause.svg)
-    skin/images/firebug/play.svg (themes/images/firebug/play.svg)
-    skin/images/firebug/rewind.svg (themes/images/firebug/rewind.svg)
-    skin/images/firebug/disable.svg (themes/images/firebug/disable.svg)
-    skin/images/firebug/breakpoint.svg (themes/images/firebug/breakpoint.svg)
-    skin/images/firebug/tool-options.svg (themes/images/firebug/tool-options.svg)
-    skin/images/firebug/debugger-step-in.svg (themes/images/firebug/debugger-step-in.svg)
-    skin/images/firebug/debugger-step-out.svg (themes/images/firebug/debugger-step-out.svg)
-    skin/images/firebug/debugger-step-over.svg (themes/images/firebug/debugger-step-over.svg)
-    skin/images/firebug/pane-collapse.svg (themes/images/firebug/pane-collapse.svg)
-    skin/images/firebug/pane-expand.svg (themes/images/firebug/pane-expand.svg)
-    skin/images/firebug/dock-undock.svg (themes/images/firebug/dock-undock.svg)
-    skin/images/firebug/dock-side.svg (themes/images/firebug/dock-side.svg)
-    skin/images/firebug/dock-bottom.svg (themes/images/firebug/dock-bottom.svg)
-    skin/images/firebug/commandline-icon.svg (themes/images/firebug/commandline-icon.svg)
-    skin/images/firebug/debugger-blackbox.svg (themes/images/firebug/debugger-blackbox.svg)
-    skin/images/firebug/debugger-prettyprint.svg (themes/images/firebug/debugger-prettyprint.svg)
-    skin/images/firebug/debugger-toggleBreakpoints.svg (themes/images/firebug/debugger-toggleBreakpoints.svg)
-    skin/images/firebug/tool-debugger-paused.svg (themes/images/firebug/tool-debugger-paused.svg)
-    skin/images/firebug/command-pick.svg (themes/images/firebug/command-pick.svg)
-    skin/images/firebug/command-console.svg (themes/images/firebug/command-console.svg)
-    skin/images/firebug/command-eyedropper.svg (themes/images/firebug/command-eyedropper.svg)
-    skin/images/firebug/command-frames.svg (themes/images/firebug/command-frames.svg)
-    skin/images/firebug/command-paintflashing.svg (themes/images/firebug/command-paintflashing.svg)
-    skin/images/firebug/command-responsivemode.svg (themes/images/firebug/command-responsivemode.svg)
-    skin/images/firebug/command-scratchpad.svg (themes/images/firebug/command-scratchpad.svg)
-    skin/images/firebug/command-screenshot.svg (themes/images/firebug/command-screenshot.svg)
-    skin/images/firebug/command-measure.svg (themes/images/firebug/command-measure.svg)
-    skin/images/firebug/command-rulers.svg (themes/images/firebug/command-rulers.svg)
-    skin/images/firebug/command-noautohide.svg (themes/images/firebug/command-noautohide.svg)
+    skin/images/read-only.svg (themes/images/read-only.svg)
 
     # Debugger
     skin/images/debugger/arrow.svg (themes/images/debugger/arrow.svg)
     skin/images/debugger/back.svg (themes/images/debugger/back.svg)
     skin/images/debugger/blackBox.svg (themes/images/debugger/blackBox.svg)
     skin/images/debugger/close.svg (themes/images/debugger/close.svg)
     skin/images/debugger/coffeescript.svg (themes/images/debugger/coffeescript.svg)
     skin/images/debugger/domain.svg (themes/images/debugger/domain.svg)

--- a/devtools/client/jsonview/test/browser_jsonview_theme.js
+++ b/devtools/client/jsonview/test/browser_jsonview_theme.js
@@ -15,19 +15,16 @@ add_task(async function() {
 
   await addJsonViewTab(TEST_JSON_URL);
 
   is(await getTheme(), "theme-light", "The initial theme is light");
 
   SpecialPowers.setCharPref("devtools.theme", "dark");
   is(await getTheme(), "theme-dark", "Theme changed to dark");
 
-  SpecialPowers.setCharPref("devtools.theme", "firebug");
-  is(await getTheme(), "theme-firebug", "Theme changed to firebug");
-
   SpecialPowers.setCharPref("devtools.theme", "light");
   is(await getTheme(), "theme-light", "Theme changed to light");
 
   SpecialPowers.setCharPref("devtools.theme", oldPref);
 });
 
 function getTheme() {
   return getElementAttr(":root", "class");

--- a/devtools/client/locales/en-US/startup.properties
+++ b/devtools/client/locales/en-US/startup.properties
@@ -17,20 +17,16 @@ options.panelLabel=Toolbox Options Panel
 # LOCALIZATION NOTE (options.darkTheme.label2)
 # Used as a label for dark theme
 options.darkTheme.label2=Dark
 
 # LOCALIZATION NOTE (options.lightTheme.label2)
 # Used as a label for light theme
 options.lightTheme.label2=Light
 
-# LOCALIZATION NOTE (options.firebugTheme.label2)
-# Used as a label for Firebug theme
-options.firebugTheme.label2=Firebug
-
 # LOCALIZATION NOTE (performance.label):
 # This string is displayed in the title of the tab when the profiler is
 # displayed inside the developer tools window and in the Developer Tools Menu.
 performance.label=Performance
 
 # LOCALIZATION NOTE (performance.panelLabel):
 # This is used as the label for the toolbox panel.
 performance.panelLabel=Performance Panel

--- a/devtools/client/netmonitor/src/assets/styles/variables.css
+++ b/devtools/client/netmonitor/src/assets/styles/variables.css
@@ -29,21 +29,16 @@
   --timing-send-color: rgba(0, 136, 204, 0.8); /* blue */
   --timing-wait-color: rgba(95, 136, 176, 0.8); /* blue grey */
   --timing-receive-color: rgba(44, 187, 15, 0.8); /* green */
 
   --sort-ascending-image: url(chrome://devtools/skin/images/sort-ascending-arrow.svg);
   --sort-descending-image: url(chrome://devtools/skin/images/sort-descending-arrow.svg);
 }
 
-:root.theme-firebug {
-  --sort-ascending-image: url(chrome://devtools/skin/images/firebug/arrow-up.svg);
-  --sort-descending-image: url(chrome://devtools/skin/images/firebug/arrow-down.svg);
-}
-
 :root {
   /* Icons */
   --play-icon-url: url("chrome://devtools/content/netmonitor/src/assets/icons/play.svg");
   --pause-icon-url: url("chrome://devtools/skin/images/pause.svg");
 
   /* HTTP status codes */
   --status-code-color-1xx: var(--theme-highlight-blue);
   --status-code-color-2xx: var(--theme-highlight-green);

--- a/devtools/client/shared/components/reps/reps.css
+++ b/devtools/client/shared/components/reps/reps.css
@@ -13,28 +13,16 @@
   --location-color: var(--theme-comment);
   --source-link-color: var(--theme-highlight-blue);
   --node-color: var(--theme-highlight-purple);
   --reference-color: var(--theme-highlight-blue);
   --comment-node-color: var(--theme-comment);
   --stack-function-color: var(--theme-highlight-red);
 }
 
-.theme-firebug {
-  --number-color: #000088;
-  --string-color: #FF0000;
-  --null-color: #787878;
-  --object-color: DarkGreen;
-  --caption-color: #444444;
-  --location-color: #555555;
-  --source-link-color: blue;
-  --node-color: rgb(0, 0, 136);
-  --reference-color: rgb(102, 102, 255);
-}
-
 /******************************************************************************/
 
 .inline {
   display: inline;
   white-space: normal;
 }
 
 .objectBox-object {

--- a/devtools/client/shared/components/tree/TreeView.css
+++ b/devtools/client/shared/components/tree/TreeView.css
@@ -4,17 +4,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 @import url('resource://devtools/client/shared/components/reps/reps.css');
 
 /******************************************************************************/
 /* TreeView Colors */
 
 :root {
-  --tree-link-color: blue;
   --tree-header-background: #C8D2DC;
   --tree-header-sorted-background: #AAC3DC;
 }
 
 /******************************************************************************/
 /* TreeView Table*/
 
 .treeTable .treeLabelCell {
@@ -155,21 +154,21 @@
   padding: 0;
 }
 
 .treeTable .treeHeaderSorted {
   background-color: var(--tree-header-sorted-background);
 }
 
 .treeTable .treeHeaderSorted > .treeHeaderCellBox {
-  background: url(chrome://devtools/skin/images/firebug/arrow-down.svg) no-repeat calc(100% - 4px);
+  background: url(chrome://devtools/skin/images/sort-descending-arrow.svg) no-repeat calc(100% - 4px);
 }
 
 .treeTable .treeHeaderSorted.sortedAscending > .treeHeaderCellBox {
-  background-image: url(chrome://devtools/skin/images/firebug/arrow-up.svg);
+  background-image: url(chrome://devtools/skin/images/sort-ascending-arrow.svg);
 }
 
 .treeTable .treeHeaderCell:hover:active {
   background-image: linear-gradient(
           rgba(0, 0, 0, 0.1),
           transparent),
       radial-gradient(1px 60% at right,
           rgba(0, 0, 0, 0.8) 0%,

--- a/devtools/client/shared/test/browser_theme.js
+++ b/devtools/client/shared/test/browser_theme.js
@@ -18,18 +18,16 @@ add_task(function* () {
 
 function testGetTheme() {
   let originalTheme = getTheme();
   ok(originalTheme, "has some theme to start with.");
   Services.prefs.setCharPref("devtools.theme", "light");
   is(getTheme(), "light", "getTheme() correctly returns light theme");
   Services.prefs.setCharPref("devtools.theme", "dark");
   is(getTheme(), "dark", "getTheme() correctly returns dark theme");
-  Services.prefs.setCharPref("devtools.theme", "firebug");
-  is(getTheme(), "firebug", "getTheme() correctly returns firebug theme");
   Services.prefs.setCharPref("devtools.theme", "unknown");
   is(getTheme(), "unknown", "getTheme() correctly returns an unknown theme");
   Services.prefs.setCharPref("devtools.theme", originalTheme);
 }
 
 function testSetTheme() {
   let originalTheme = getTheme();
   // Put this in a variable rather than hardcoding it because the default
@@ -43,47 +41,39 @@ function testSetTheme() {
       "A preference event triggered by setTheme comes after the value is set.");
   });
   setTheme(otherTheme);
   is(Services.prefs.getCharPref("devtools.theme"), otherTheme,
      "setTheme() correctly sets another theme.");
   setTheme(originalTheme);
   is(Services.prefs.getCharPref("devtools.theme"), originalTheme,
      "setTheme() correctly sets the original theme.");
-  setTheme("firebug");
-  is(Services.prefs.getCharPref("devtools.theme"), "firebug",
-     "setTheme() correctly sets firebug theme.");
   setTheme("unknown");
   is(Services.prefs.getCharPref("devtools.theme"), "unknown",
      "setTheme() correctly sets an unknown theme.");
   Services.prefs.setCharPref("devtools.theme", originalTheme);
 
   prefObserver.destroy();
 }
 
 function testGetColor() {
   let BLUE_DARK = "#75BFFF";
   let BLUE_LIGHT = "#0074e8";
-  let BLUE_FIREBUG = "#3455db";
   let originalTheme = getTheme();
 
   setTheme("dark");
   is(getColor("highlight-blue"), BLUE_DARK, "correctly gets color for enabled theme.");
   setTheme("light");
   is(getColor("highlight-blue"), BLUE_LIGHT, "correctly gets color for enabled theme.");
-  setTheme("firebug");
-  is(getColor("highlight-blue"), BLUE_FIREBUG, "correctly gets color for enabled theme.");
   setTheme("metal");
   is(getColor("highlight-blue"), BLUE_LIGHT,
      "correctly uses light for default theme if enabled theme not found");
 
   is(getColor("highlight-blue", "dark"), BLUE_DARK,
      "if provided and found, uses the provided theme.");
-  is(getColor("highlight-blue", "firebug"), BLUE_FIREBUG,
-     "if provided and found, uses the provided theme.");
   is(getColor("highlight-blue", "metal"), BLUE_LIGHT,
      "if provided and not found, defaults to light theme.");
   is(getColor("somecomponents"), null, "if a type cannot be found, should return null.");
 
   setTheme(originalTheme);
 }
 
 function testColorExistence() {
@@ -95,11 +85,10 @@ function testColorExistence() {
     "content-color3", "highlight-green", "highlight-blue", "highlight-bluegrey",
     "highlight-purple", "highlight-lightorange", "highlight-orange", "highlight-red",
     "highlight-pink"
   ];
 
   for (let type of vars) {
     ok(getColor(type, "light"), `${type} is a valid color in light theme`);
     ok(getColor(type, "dark"), `${type} is a valid color in dark theme`);
-    ok(getColor(type, "firebug"), `${type} is a valid color in firebug theme`);
   }
 }

--- a/devtools/client/shared/theme.js
+++ b/devtools/client/shared/theme.js
@@ -11,17 +11,16 @@
 
 const Services = require("Services");
 
 const variableFileContents = require("theme-loader!devtools/client/themes/variables.css");
 
 const THEME_SELECTOR_STRINGS = {
   light: ":root.theme-light {",
   dark: ":root.theme-dark {",
-  firebug: ":root.theme-firebug {",
   root: ":root {",
 };
 const THEME_PREF = "devtools.theme";
 
 /**
  * Takes a theme name and returns the contents of its variable rule block.
  * The first time this runs fetches the variables CSS file and caches it.
  */

--- a/devtools/client/themes/animation.css
+++ b/devtools/client/themes/animation.css
@@ -25,23 +25,16 @@
   --tick-line-style: 0.5px solid rgba(128, 136, 144, 0.5);
 }
 
 :root.theme-dark {
   --animation-even-background-color: rgba(255, 255, 255, 0.05);
   --keyframe-marker-shadow-color: #818181;
 }
 
-:root.theme-firebug {
-  --command-pick-image: url(chrome://devtools/skin/images/firebug/command-pick.svg);
-  --pause-image: url(chrome://devtools/skin/images/firebug/pause.svg);
-  --resume-image: url(chrome://devtools/skin/images/firebug/play.svg);
-  --rewind-image: url(chrome://devtools/skin/images/firebug/rewind.svg);
-}
-
 /* Root element of animation inspector */
 #animation-container {
   display: flex;
   flex-direction: column;
   height: 100%;
 }
 
 #animation-container .uncontrolled {

--- a/devtools/client/themes/animationinspector.css
+++ b/devtools/client/themes/animationinspector.css
@@ -28,25 +28,16 @@
   --even-animation-timeline-background-color: rgba(128,128,128,0.03);
   --command-pick-image: url(chrome://devtools/skin/images/command-pick.svg);
   --pause-image: url(chrome://devtools/skin/images/pause.svg);
   --rewind-image: url(chrome://devtools/skin/images/rewind.svg);
   --play-image: url(chrome://devtools/skin/images/play.svg);
   --close-button-image: url(chrome://devtools/skin/images/close.svg);
 }
 
-.theme-firebug {
-  --even-animation-timeline-background-color: rgba(128,128,128,0.03);
-  --command-pick-image: url(chrome://devtools/skin/images/firebug/command-pick.svg);
-  --pause-image: url(chrome://devtools/skin/images/firebug/pause.svg);
-  --rewind-image: url(chrome://devtools/skin/images/firebug/rewind.svg);
-  --play-image: url(chrome://devtools/skin/images/firebug/play.svg);
-  --close-button-image: url(chrome://devtools/skin/images/firebug/close.svg);
-}
-
 .theme-light {
   /* The color for animation type 'opacity' */
   --opacity-border-color: var(--theme-highlight-pink);
   --opacity-background-color: #b82ee580;
   /* The color for animation type 'transform' */
   --transform-border-color: var(--theme-graphs-orange);
   --transform-background-color: #efc05280;
   /* The color for other animation type */

--- a/devtools/client/themes/common.css
+++ b/devtools/client/themes/common.css
@@ -22,25 +22,20 @@
 :root[platform="mac"] {
   --monospace-font-family: Menlo, monospace;
 }
 
 :root[platform="win"] {
   --monospace-font-family: Consolas, monospace;
 }
 
-:root[platform="linux"],
-:root.theme-firebug {
+:root[platform="linux"] {
   --monospace-font-family: monospace;
 }
 
-:root.theme-firebug {
-  --proportional-font-family: Lucida Grande, Tahoma, sans-serif;
-}
-
 .devtools-monospace {
   font-family: var(--monospace-font-family);
 }
 
 :root[platform="linux"] .devtools-monospace {
   font-size: 11px;
 }
 

deleted file mode 100644
--- a/devtools/client/themes/firebug-theme.css
+++ /dev/null
@@ -1,57 +0,0 @@
-/* vim:set ts=2 sw=2 sts=2 et: */
-/* 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/. */
-
-@import url(resource://devtools/client/themes/variables.css);
-@import url(resource://devtools/client/themes/common.css);
-@import url(chrome://devtools/skin/light-theme.css);
-
-:root.theme-firebug {
-  font-size: 11px;
-  font-family: var(--proportional-font-family);
-}
-
-/* CodeMirror Color Syntax */
-
-.theme-firebug .cm-keyword {color: BlueViolet; font-weight: bold;}
-.theme-firebug .cm-atom {color: #219;}
-.theme-firebug .cm-number {color: #164;}
-.theme-firebug .cm-def {color: #00f;}
-.theme-firebug .cm-variable {color: black;}
-.theme-firebug .cm-variable-2 {color: black;}
-.theme-firebug .cm-variable-3 {color: black;}
-.theme-firebug .cm-property {color: black;}
-.theme-firebug .cm-operator {color: black;}
-.theme-firebug .cm-comment {color: Silver;}
-.theme-firebug .cm-string {color: Red;}
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deleted file mode 100644
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deleted file mode 100644
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deleted file mode 100644
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deleted file mode 100644
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deleted file mode 100644
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deleted file mode 100644
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-      <stop offset="0" stop-color="#f5a742"/>
-      <stop offset="1" stop-color="#f9cb8a"/>
-    </linearGradient>
-    <linearGradient x1="4.779" y1="1048.788" x2="3.117" y2="1039.853" id="e" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.993 0 0 .998 .028 2.025)"/>
-    <linearGradient x1="5.527" y1="1049.91" x2="2.514" y2="1038.877" id="f" xlink:href="#b" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.993 0 0 .998 .028 2.025)"/>
-    <linearGradient id="c">
-      <stop offset="0" stop-color="#f5a742"/>
-      <stop offset="1" stop-color="#f9cb8a"/>
-    </linearGradient>
-    <linearGradient id="d">
-      <stop offset="0" stop-color="#dd8506"/>
-      <stop offset="1" stop-color="#f9c06e" stop-opacity=".988"/>
-    </linearGradient>
-    <linearGradient x1="4.779" y1="1048.788" x2="3.117" y2="1039.853" id="g" xlink:href="#c" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.993 0 0 .998 7.028 2.025)"/>
-    <linearGradient x1="5.527" y1="1049.91" x2="2.514" y2="1038.877" id="h" xlink:href="#d" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.993 0 0 .998 7.028 2.025)"/>
-  </defs>
-  <g stroke-linejoin="round">
-    <path fill="url(#e)" stroke="url(#f)" d="M2.5 1038.862h3v11h-3z" transform="translate(0 -1036.362)"/>
-    <path fill="url(#g)" stroke="url(#h)" d="M9.5 1038.862h3v11h-3z" transform="translate(0 -1036.362)"/>
-  </g>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/play.svg
+++ /dev/null
@@ -1,18 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="16" height="16">
-  <defs>
-    <linearGradient id="b">
-      <stop offset="0" stop-color="#2959b8"/>
-      <stop offset="1" stop-color="#83ace8"/>
-    </linearGradient>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#5c87d0"/>
-      <stop offset="1" stop-color="#abc7ed"/>
-    </linearGradient>
-    <linearGradient x1="1.472" y1="-4.098" x2="1.472" y2="6.772" id="c" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.65609 0 0 -1.01925 4.494 9.401)"/>
-    <linearGradient x1="10.18" y1="8.767" x2="3.926" y2="2.99" id="d" xlink:href="#b" gradientUnits="userSpaceOnUse"/>
-  </defs>
-  <path d="M11.788 8L4.5 1.204v13.592z" fill="url(#c)" stroke="url(#d)" stroke-linejoin="round"/>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/rewind.svg
+++ /dev/null
@@ -1,18 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="16" height="16">
-  <defs>
-    <linearGradient id="b">
-      <stop offset="0" stop-color="#2959b8"/>
-      <stop offset="1" stop-color="#83ace8"/>
-    </linearGradient>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#5c87d0"/>
-      <stop offset="1" stop-color="#abc7ed"/>
-    </linearGradient>
-    <linearGradient x1="1.472" y1="-4.098" x2="1.472" y2="6.772" id="c" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="matrix(.65609 0 0 -1.01925 4.494 9.401)"/>
-    <linearGradient x1="10.18" y1="8.767" x2="3.926" y2="2.99" id="d" xlink:href="#b" gradientUnits="userSpaceOnUse"/>
-  </defs>
-  <path d="M11.788 8L4.5 1.204v13.592z" transform="matrix(-1 0 0 1 16 0)" fill="url(#c)" stroke="url(#d)" stroke-linejoin="round"/>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/tool-debugger-paused.svg
+++ /dev/null
@@ -1,14 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="11" height="12">
-  <defs>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#b4aa00"/>
-      <stop offset=".659" stop-color="#f5e600"/>
-      <stop offset="1" stop-color="#f5e600"/>
-    </linearGradient>
-    <linearGradient x1="1.256" y1="6.226" x2=".157" y2=".942" id="b" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="matrix(1.1625 0 0 1.2744 1.663 1040.82)"/>
-  </defs>
-  <path d="M8.553 1046.88l-2.742 1.735c-4.951 3.273-5.215 3.09-5.215.035v-6.845c0-2.706.26-2.927 5.215.208l2.593 1.641c2.642 1.553 2.642 1.648.149 3.226z" fill="url(#b)" stroke-width="1.217" stroke-linejoin="round" transform="matrix(1 0 0 .95762 0 -995.06)" stroke="#888000"/>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/tool-options.svg
+++ /dev/null
@@ -1,18 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="16" height="16" viewBox="0 0 16 16">
-  <defs>
-    <linearGradient id="b">
-      <stop offset="0" stop-color="#464f5a"/>
-      <stop offset="1" stop-color="#7e8b9a"/>
-    </linearGradient>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#6a7786"/>
-      <stop offset="1" stop-color="#abb3bd"/>
-    </linearGradient>
-    <linearGradient xlink:href="#a" id="c" x1="13.108" y1="13.135" x2="2.763" y2="2.791" gradientUnits="userSpaceOnUse" gradientTransform="translate(.306 1036.661) scale(.9618)"/>
-    <linearGradient xlink:href="#b" id="d" x1="14.815" y1="11.602" x2="4.34" y2="1.127" gradientUnits="userSpaceOnUse" gradientTransform="translate(.306 1036.661) scale(.9618)"/>
-  </defs>
-  <path style="marker:none" d="M7.23 1036.661c-.426 0-.665.445-.768.962l-.25 1.25a5.77 5.77 0 0 0-.825.345l-1.063-.71c-.477-.205-.924-.437-1.225-.135l-1.088 1.087c-.301.302-.157.786.136 1.225l.706 1.062a5.77 5.77 0 0 0-.333.824l-1.258.252c-.482.193-.962.344-.962.77v1.538c0 .427.445.665.962.769l1.258.252a5.77 5.77 0 0 0 .34.815l-.713 1.073c-.205.477-.437.92-.136 1.223l1.088 1.089c.301.301.786.155 1.225-.137l1.069-.712a5.77 5.77 0 0 0 .815.33l.254 1.268c.192.482.342.962.768.962h1.54c.426 0 .665-.445.768-.962l.254-1.264a5.77 5.77 0 0 0 .81-.338l1.074.716c.477.204.924.438 1.225.137l1.088-1.09c.301-.301.157-.784-.136-1.222l-.71-1.067a5.77 5.77 0 0 0 .333-.821l1.262-.252c.482-.193.962-.342.962-.769v-1.538c0-.426-.445-.667-.962-.77l-1.253-.252a5.77 5.77 0 0 0-.342-.819l.71-1.067c.205-.477.437-.923.136-1.225l-1.088-1.087c-.301-.302-.786-.158-1.225.135l-1.057.706a5.77 5.77 0 0 0-.829-.336l-.252-1.255c-.192-.482-.342-.962-.768-.962H7.23zm.77 4.81a2.885 2.885 0 0 1 2.885 2.885A2.885 2.885 0 0 1 8 1047.24a2.885 2.885 0 0 1-2.885-2.885A2.885 2.885 0 0 1 8 1041.47z" color="#000" overflow="visible" fill="url(#c)" stroke="url(#d)" stroke-width=".6" stroke-linejoin="round" transform="translate(0 -1036.362)"/>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/twisty-closed-firebug.svg
+++ /dev/null
@@ -1,14 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="11" height="11">
-  <defs>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#c3baaa"/>
-      <stop offset="1" stop-color="#fff"/>
-    </linearGradient>
-    <linearGradient x1="6.053" y1="7.093" x2="2.888" y2="1.8" id="b" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="translate(.885 .885) scale(1.02564)"/>
-  </defs>
-  <rect width="8" height="8" rx="1" ry="1" x="1.5" y="1.5" fill="url(#b)" stroke="#7898b5" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M5 3v2H3v1h2v2h1V6h2V5H6V3H5z"/>
-</svg>

deleted file mode 100644
--- a/devtools/client/themes/images/firebug/twisty-open-firebug.svg
+++ /dev/null
@@ -1,14 +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/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="11" height="11">
-  <defs>
-    <linearGradient id="a">
-      <stop offset="0" stop-color="#c3baaa"/>
-      <stop offset="1" stop-color="#fff"/>
-    </linearGradient>
-    <linearGradient x1="6.053" y1="7.093" x2="2.888" y2="1.8" id="b" xlink:href="#a" gradientUnits="userSpaceOnUse" gradientTransform="translate(.885 .885) scale(1.02564)"/>
-  </defs>
-  <rect width="8" height="8" rx="1" ry="1" x="1.5" y="1.5" fill="url(#b)" stroke="#7898b5" stroke-linecap="round" stroke-linejoin="round"/>
-  <path d="M3 5h5v1H3z"/>
-</svg>

rename from devtools/client/themes/images/firebug/read-only.svg
rename to devtools/client/themes/images/read-only.svg

--- a/devtools/client/themes/inspector.css
+++ b/devtools/client/themes/inspector.css
@@ -2,20 +2,16 @@
 /* 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/. */
 
 :root {
   --eyedropper-image: url(images/command-eyedropper.svg);
 }
 
-.theme-firebug {
-  --eyedropper-image: url(images/firebug/command-eyedropper.svg);
-}
-
 * {
   box-sizing: border-box;
 }
 
 /* Make sure to hide scroll bars for the parent window */
 window {
   overflow: hidden;
 }

--- a/devtools/client/themes/performance.css
+++ b/devtools/client/themes/performance.css
@@ -15,24 +15,16 @@
 .theme-light {
   --cell-border-color: rgba(0,0,0,0.15);
   --cell-border-color-light: rgba(0,0,0,0.1);
   --focus-cell-border-color: rgba(0,0,0,0.3);
   --row-alt-background-color: rgba(76,158,217,0.1);
   --row-hover-background-color: rgba(76,158,217,0.2);
 }
 
-.theme-firebug {
-  --cell-border-color: rgba(0,0,0,0.15);
-  --cell-border-color-light: rgba(0,0,0,0.1);
-  --focus-cell-border-color: rgba(0,0,0,0.3);
-  --row-alt-background-color: rgba(76,158,217,0.1);
-  --row-hover-background-color: rgba(76,158,217,0.2);
-}
-
 /*
  * DE-XUL: Set a sidebar width because inline XUL components will cause the flex
  * to overflow if dynamically sized.
  */
 .performance-tool {
   --sidebar-width: 185px;
 }
 

--- a/devtools/client/themes/rules.css
+++ b/devtools/client/themes/rules.css
@@ -14,24 +14,16 @@
 :root.theme-dark {
   --rule-highlight-background-color: #521C76;
   --rule-overridden-item-border-color: var(--theme-content-color1);
   --rule-header-background-color: #222225;
   --rule-flex-toggle-color: var(--grey-10);
   --rule-shape-toggle-color: var(--grey-10);
 }
 
-:root.theme-firebug {
-  --rule-highlight-background-color: var(--theme-highlight-yellow);
-  --rule-property-name: darkgreen;
-  --rule-property-value: darkblue;
-  --rule-overridden-item-border-color: var(--theme-content-color2);
-  --rule-header-background-color: var(--theme-header-background);
-}
-
 /* Rule View Tabpanel */
 
 #sidebar-panel-ruleview {
   margin: 0;
   display: flex;
   flex-direction: column;
   width: 100%;
   height: 100%;

--- a/devtools/client/themes/toolbars.css
+++ b/devtools/client/themes/toolbars.css
@@ -25,22 +25,16 @@
 
   --magnifying-glass-image: url(chrome://devtools/skin/images/search.svg);
   --filter-image: url(chrome://devtools/skin/images/filter.svg);
   --tool-options-image: url(chrome://devtools/skin/images/tool-options.svg);
 
   --separator-border-image: linear-gradient(transparent 4px, rgba(100%,100%,100%,.2) 4px, rgba(100%,100%,100%,.2) calc(100% - 4px), transparent calc(100% - 4px));
 }
 
-.theme-firebug {
-  --magnifying-glass-image: url(chrome://devtools/skin/images/search.svg);
-  --tool-options-image: url(chrome://devtools/skin/images/firebug/tool-options.svg);
-}
-
-
 /* Toolbars */
 .devtools-toolbar,
 .devtools-sidebar-tabs tabs {
   -moz-appearance: none;
   padding: 0;
   border-width: 0;
   border-bottom-width: 1px;
   border-style: solid;

--- a/devtools/client/themes/toolbox.css
+++ b/devtools/client/themes/toolbox.css
@@ -17,34 +17,16 @@
   --command-pick-accessibility-image: url(images/command-pick-accessibility.svg);
   --command-frames-image: url(images/command-frames.svg);
   --command-splitconsole-image: url(images/command-console.svg);
   --command-noautohide-image: url(images/command-noautohide.svg);
   --command-rulers-image: url(images/command-rulers.svg);
   --command-measure-image: url(images/command-measure.svg);
 }
 
-.theme-firebug {
-  --close-button-image: url(chrome://devtools/skin/images/firebug/close.svg);
-  --dock-bottom-image: url(chrome://devtools/skin/images/firebug/dock-bottom.svg);
-  --dock-side-image: url(chrome://devtools/skin/images/firebug/dock-side.svg);
-  --dock-undock-image: url(chrome://devtools/skin/images/firebug/dock-undock.svg);
-
-  --command-paintflashing-image: url(images/firebug/command-paintflashing.svg);
-  --command-screenshot-image: url(images/firebug/command-screenshot.svg);
-  --command-responsive-image: url(images/firebug/command-responsivemode.svg);
-  --command-scratchpad-image: url(images/firebug/command-scratchpad.svg);
-  --command-pick-image: url(images/firebug/command-pick.svg);
-  --command-frames-image: url(images/firebug/command-frames.svg);
-  --command-splitconsole-image: url(images/firebug/command-console.svg);
-  --command-noautohide-image: url(images/firebug/command-noautohide.svg);
-  --command-rulers-image: url(images/firebug/command-rulers.svg);
-  --command-measure-image: url(images/firebug/command-measure.svg);
-}
-
 /* Toolbox tabbar */
 
 .devtools-tabbar {
   -moz-appearance: none;
   display: flex;
   background: var(--theme-tab-toolbar-background);
   border-bottom: 1px solid var(--theme-splitter-color);
   box-sizing: border-box;

--- a/devtools/client/themes/variables.css
+++ b/devtools/client/themes/variables.css
@@ -181,95 +181,16 @@
   /* Command line */
   --theme-command-line-image: url(chrome://devtools/skin/images/commandline-icon.svg#dark-theme);
   --theme-command-line-image-focus: url(chrome://devtools/skin/images/commandline-icon.svg#dark-theme-focus);
 
   --theme-codemirror-gutter-background: #262b37;
   --theme-messageCloseButtonFilter: invert(1);
 }
 
-:root.theme-firebug {
-  --theme-body-background: #fff;
-  --theme-sidebar-background: #fcfcfc;
-  --theme-contrast-background: #e6b064;
-
-  --theme-tab-toolbar-background: rgb(240, 240, 240) linear-gradient(rgba(255, 255, 255, 0.8), transparent);
-  --theme-toolbar-background: rgb(240, 240, 240) linear-gradient(rgba(255, 255, 255, 0.8), transparent);
-  --theme-toolbar-tab-selected-background: rgb(253, 253, 253);
-  --theme-selection-background: #3399ff;
-  --theme-selection-background-hover: rgba(128,128,128,0.2);
-  --theme-selection-color: white;
-  --theme-splitter-color: #bfbfbf;
-  --theme-comment: darkgreen;
-
-  --theme-body-color: #252525;
-  --theme-body-color-alt: #585959;
-  --theme-content-color1: #292e33;
-  --theme-content-color2: #8fa1b2;
-  --theme-content-color3: #667380;
-
-  --theme-highlight-green: #2cbb0f;
-  --theme-highlight-blue: #3455db;
-  --theme-highlight-bluegrey: #0072ab;
-  --theme-highlight-purple: #000080;
-  --theme-highlight-lightorange: #d97e00;
-  --theme-highlight-orange: #f13c00;
-  --theme-highlight-red: #f00;
-  --theme-highlight-pink: #b82ee5;
-  --theme-highlight-gray: #dde1e4;
-
-  /* Colors used in Graphs, like performance tools. Similar colors to Chrome's timeline. */
-  --theme-graphs-green: #85d175;
-  --theme-graphs-blue: #83b7f6;
-  --theme-graphs-bluegrey: #0072ab;
-  --theme-graphs-purple: #b693eb;
-  --theme-graphs-yellow: #efc052;
-  --theme-graphs-orange: #d97e00;
-  --theme-graphs-red: #e57180;
-  --theme-graphs-grey: #cccccc;
-  --theme-graphs-full-red: #f00;
-  --theme-graphs-full-blue: #00f;
-
-  /* Images */
-  --theme-pane-collapse-image: url(chrome://devtools/skin/images/firebug/pane-collapse.svg);
-  --theme-pane-expand-image: url(chrome://devtools/skin/images/firebug/pane-expand.svg);
-
-  /* Icon filters */
-  --theme-icon-checked-filter: url(chrome://devtools/skin/images/filters.svg#icon-checked-light);
-
-  /* Font size */
-  --theme-toolbar-font-size: 12px;
-
-  /* Header */
-  --theme-header-background: #F0F0F0 linear-gradient(to top,
-                                                     rgba(0, 0, 0, 0.1),
-                                                     transparent) repeat-x;
-
-  /* Command line */
-  --theme-command-line-image: url(chrome://devtools/skin/images/firebug/commandline-icon.svg);
-  --theme-command-line-image-focus: url(chrome://devtools/skin/images/firebug/commandline-icon.svg#focus);
-
-  /* Toolbar buttons */
-  --toolbarbutton-background: transparent linear-gradient(rgba(255, 255, 255, 0.4), rgba(255, 255, 255, 0.2)) no-repeat;
-  --toolbarbutton-hover-background: transparent;
-  --toolbarbutton-hover-border-color: var(--theme-splitter-color);
-  --toolbarbutton-checked-background: linear-gradient(rgba(0, 0, 0, 0.1), transparent);
-  --toolbarbutton-checked-color: var(--theme-body-color);
-  --toolbarbutton-checked-border-color: var(--toolbarbutton-hover-border-color);
-
-  --theme-codemirror-gutter-background: #ebeced;
-}
-
-:root.theme-firebug[platform="win"] {
-  --theme-tab-toolbar-background: #d8eaf9 linear-gradient(rgba(253, 253, 253, 0.2), rgba(253, 253, 253, 0));
-  --theme-toolbar-background: #d8eaf9 linear-gradient(rgba(255, 255, 255, 0.8), rgba(255, 255, 255, 0.2));
-  --theme-toolbar-tab-selected-background: rgb(247, 251, 254);
-  --theme-splitter-color: #aabccf;
-}
-
 :root {
   --theme-focus-border-color-textbox: #0675d3;
   --theme-textbox-box-shadow: rgba(97,181,255,.75);
 
   /* For accessibility purposes we want to enhance the focus styling. This
    * should improve keyboard navigation usability. */
   --theme-focus-outline: 1px dotted var(--theme-focus-outline-color);
   --theme-focus-box-shadow-textbox: 0 0 0 1px var(--theme-textbox-box-shadow);

--- a/devtools/client/themes/widgets.css
+++ b/devtools/client/themes/widgets.css
@@ -18,25 +18,16 @@
   --table-splitter-color: rgba(0,0,0,0.15);
   --table-zebra-background: rgba(0,0,0,0.05);
   --sidemenu-selected-arrow: url(images/item-arrow-ltr.svg);
   --sidemenu-selected-arrow-rtl: url(images/item-arrow-rtl.svg);
   --delete-icon: url(chrome://devtools/skin/images/vview-delete.png);
   --delete-icon-2x: url(chrome://devtools/skin/images/vview-delete@2x.png);
 }
 
-.theme-firebug {
-  --table-splitter-color: rgba(0,0,0,0.15);
-  --table-zebra-background: rgba(0,0,0,0.05);
-  --sidemenu-selected-arrow: url(images/item-arrow-ltr.svg);
-  --sidemenu-selected-arrow-rtl: url(images/item-arrow-rtl.svg);
-  --delete-icon: url(chrome://devtools/skin/images/firebug/close.svg);
-  --delete-icon-2x: url(chrome://devtools/skin/images/firebug/close.svg);
-}
-
 /* Generic pane helpers */
 
 .generic-toggled-pane {
   margin-inline-start: 0 !important;
   /* Unfortunately, transitions don't work properly with locale-aware properties,
      so both the left and right margins are set via js, while the start margin
      is always overridden here. */
 }

--- a/devtools/docs/contributing/css.md
+++ b/devtools/docs/contributing/css.md
@@ -51,33 +51,30 @@ Also:
 
 Naming standards for class names:
 
 * `lower-case-with-dashes` is the most common.
 * But `camelCase` is also used sometimes. Try to follow the style of existing or related code.
 
 ## Light and Dark theme support
 
-DevTools supports 3 different themes: the dark theme, the light theme and the firebug theme. In order to support them, there are 3 class names available (`theme-dark`, `theme-light` and `theme-firebug`).
+DevTools supports 2 different themes: the dark theme and the light theme. In order to support them, there are 2 class names available (`theme-dark` and `theme-light`).
 
 * Use [pre-defined CSS variables](https://developer.mozilla.org/en-US/docs/Tools/DevToolsColors) instead of hardcoding colors when possible.
 * If you need to support themes and the pre-defined variables don't fit, define a variable with your custom colors at the beginning of the CSS file. This avoids selector duplication in the code.
 
 Example:
 
 ```css
 .theme-light {
   --some-variable-name: <color-for-light-theme>;
 }
 .theme-dark {
   --some-variable-name: <color-for-dark-theme>;
 }
-.theme-firebug {
-  --some-variable-name: <color-for-dark-theme>;
-}
 #myElement {
   background-color: var(--some-variable-name);
 }
 ```
 
 ## HDPI support
 
 It's recommended to use SVG since it keeps the CSS clean when supporting multiple resolutions. However, if only 1x and 2x PNG assets are available, you can use this `@media` query to target higher density displays (HDPI): `@media (min-resolution: 1.1dppx)`. <!--TODO an example would be good here-->