--- a/devtools/client/jar.mn
+++ b/devtools/client/jar.mn
@@ -199,17 +199,16 @@ devtools.jar:
     skin/images/debugger-toggleBreakpoints.svg (themes/images/debugger-toggleBreakpoints.svg)
     skin/images/dock-bottom.svg (themes/images/dock-bottom.svg)
     skin/images/dock-side-left.svg (themes/images/dock-side-left.svg)
     skin/images/dock-side-right.svg (themes/images/dock-side-right.svg)
     skin/images/dock-undock.svg (themes/images/dock-undock.svg)
     skin/images/jump-definition.svg (themes/images/jump-definition.svg)
     skin/images/tracer-icon.png (themes/images/tracer-icon.png)
     skin/images/tracer-icon@2x.png (themes/images/tracer-icon@2x.png)
-    skin/floating-scrollbars-dark-theme.css (themes/floating-scrollbars-dark-theme.css)
     skin/floating-scrollbars-responsive-design.css (themes/floating-scrollbars-responsive-design.css)
     skin/inspector.css (themes/inspector.css)
     skin/images/profiler-stopwatch.svg (themes/images/profiler-stopwatch.svg)
     skin/images/debugging-addons.svg (themes/images/debugging-addons.svg)
     skin/images/debugging-tabs.svg (themes/images/debugging-tabs.svg)
     skin/images/debugging-workers.svg (themes/images/debugging-workers.svg)
     skin/images/globe.svg (themes/images/globe.svg)
     skin/images/sad-face.svg (themes/images/sad-face.svg)

--- a/devtools/client/shared/theme-switching.js
+++ b/devtools/client/shared/theme-switching.js
@@ -28,32 +28,16 @@
   // to have per-platform CSS working correctly.
   if (documentElement.getAttribute("no-theme") === "true") {
     return;
   }
 
   const devtoolsStyleSheets = new WeakMap();
   let gOldTheme = "";
 
-  function forceStyle() {
-    const computedStyle = window.getComputedStyle(documentElement);
-    if (!computedStyle) {
-      // Null when documentElement is not ready. This method is anyways not
-      // required then as scrollbars would be in their state without flushing.
-      return;
-    }
-    // Save display value
-    const display = computedStyle.display;
-    documentElement.style.display = "none";
-    // Flush
-    window.getComputedStyle(documentElement).display;
-    // Restore
-    documentElement.style.display = display;
-  }
-
   /*
    * Notify the window that a theme switch finished so tests can check the DOM
    */
   function notifyWindow() {
     window.dispatchEvent(new CustomEvent("theme-switch-complete", {}));
   }
 
   /*
@@ -84,36 +68,16 @@
 
     const loadEvents = [];
     for (const url of newThemeDef.stylesheets) {
       const {styleSheet, loadPromise} = appendStyleSheet(document, url);
       devtoolsStyleSheets.get(newThemeDef).push(styleSheet);
       loadEvents.push(loadPromise);
     }
 
-    if (os !== "win" && os !== "mac") {
-      // Windows & Mac always use native scrollbars, Linux still uses custom floating
-      // scrollbar implementation.
-      try {
-        const StylesheetUtils = require("devtools/shared/layout/utils");
-        const SCROLLBARS_URL = "chrome://devtools/skin/floating-scrollbars-dark-theme.css";
-        if (!Services.appShell.hiddenDOMWindow
-          .matchMedia("(-moz-overlay-scrollbars)").matches) {
-          if (newTheme == "dark") {
-            StylesheetUtils.loadSheet(window, SCROLLBARS_URL, "agent");
-          } else if (oldTheme == "dark") {
-            StylesheetUtils.removeSheet(window, SCROLLBARS_URL, "agent");
-          }
-          forceStyle();
-        }
-      } catch (e) {
-        console.warn("customize scrollbar styles is only supported in firefox");
-      }
-    }
-
     Promise.all(loadEvents).then(() => {
       // Unload all stylesheets and classes from the old theme.
       if (oldThemeDef) {
         for (const name of oldThemeDef.classList) {
           documentElement.classList.remove(name);
         }
 
         for (const sheet of devtoolsStyleSheets.get(oldThemeDef) || []) {

--- a/devtools/client/sourceeditor/codemirror/mozilla.css
+++ b/devtools/client/sourceeditor/codemirror/mozilla.css
@@ -84,32 +84,16 @@
   cursor: text;
   height: 100%;
 }
 
 .CodeMirror-gutters {
   cursor: default;
 }
 
-/* This is to avoid the fake horizontal scrollbar div of codemirror to go 0
-height when floating scrollbars are active. Make sure that this value is equal
-to the maximum of `min-height` specific to the `scrollbar[orient="horizontal"]`
-selector in floating-scrollbar-light.css across all platforms. */
-.CodeMirror-hscrollbar {
-  min-height: 10px;
-}
-
-/* This is to avoid the fake vertical scrollbar div of codemirror to go 0
-width when floating scrollbars are active. Make sure that this value is equal
-to the maximum of `min-width` specific to the `scrollbar[orient="vertical"]`
-selector in floating-scrollbar-light.css across all platforms. */
-.CodeMirror-vscrollbar {
-  min-width: 10px;
-}
-
 .cm-trailingspace {
   background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAACCAYAAAB/qH1jAAAABmJLR0QA/wD/AP+gvaeTAAAACXBIWXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH3QUXCToH00Y1UgAAACFJREFUCNdjPMDBUc/AwNDAAAFMTAwMDA0OP34wQgX/AQBYgwYEx4f9lQAAAABJRU5ErkJggg==");
   opacity: 0.75;
   background-position: left bottom;
   background-repeat: repeat-x;
 }
 
 .cm-highlight {

--- a/devtools/client/themes/common.css
+++ b/devtools/client/themes/common.css
@@ -33,16 +33,32 @@
 :root[platform="win"] {
   --monospace-font-family: Consolas, monospace;
 }
 
 :root[platform="linux"] {
   --monospace-font-family: monospace;
 }
 
+/**
+ * Customize the dark theme's scrollbar colors to avoid excessive contrast.
+ */
+:root.theme-dark {
+  scrollbar-color: var(--theme-body-color-inactive) var(--theme-splitter-color);
+}
+
+/**
+ * Customize scrollbar colors on Linux + light theme, to avoid visual conflicts
+ * between the light theme and the selected GTK theme (see bug 1471163).
+ * This removes GTK scrollbars and uses a fallback design (see bug 1464723).
+ */
+:root[platform="linux"].theme-light {
+  scrollbar-color: var(--theme-body-color-inactive) var(--grey-20);
+}
+
 .devtools-monospace {
   font-family: var(--monospace-font-family);
   font-size: var(--theme-code-font-size);
 }
 
 /**
  * Override wrong system font from forms.css
  * Bug 1458224: buttons use a wrong default font-size on Linux

--- a/devtools/client/themes/dark-theme.css
+++ b/devtools/client/themes/dark-theme.css
@@ -22,23 +22,16 @@ body {
   color: var(--theme-body-color);
 }
 
 ::-moz-selection {
   background-color: var(--theme-selection-background);
   color: var(--theme-selection-color);
 }
 
-:root[platform="win"],
-:root[platform="mac"] {
-  /* Set colors for native scrollbars on Windows dark theme */
-  /* Other platforms support for scrollbar theming is Bug 1460109 */
-  scrollbar-color: var(--theme-body-color-inactive) var(--theme-splitter-color);
-}
-
 .theme-selected,
 .CodeMirror-hint-active {
   background-color: var(--theme-selection-background);
   color: var(--theme-selection-color);
 }
 
 .theme-bg-contrast,
 .variable-or-property:not([overridden])[changed] {

deleted file mode 100644
--- a/devtools/client/themes/floating-scrollbars-dark-theme.css
+++ /dev/null
@@ -1,55 +0,0 @@
-@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
-@namespace html url("http://www.w3.org/1999/xhtml");
-
-/* Restrict all styles to `*|*:not(html|select) > scrollbar` so that scrollbars
-   inside a <select> are excluded (including them hides the select arrow on
-   Windows).  We want to include both the root scrollbars for the document as
-   well as any overflow: scroll elements within the page, while excluding
-   <select>. */
-*|*:not(html|select) > scrollbar {
-  -moz-appearance: none !important;
-  position: relative;
-  background-color: transparent;
-  background-image: none;
-  z-index: 2147483647;
-  padding: 2px;
-  pointer-events: auto;
-}
-
-*|*:root[platform="mac"] > scrollbar,
-*|*:root[platform="mac"] *|*:not(html|select) > scrollbar {
-  border: none;
-}
-
-/* Scrollbar code will reset the margin to the correct side depending on
-   where layout actually puts the scrollbar */
-*|*:not(html|select) > scrollbar[orient="vertical"] {
-  margin-left: -10px;
-  min-width: 10px;
-  max-width: 10px;
-}
-
-*|*:not(html|select) > scrollbar[orient="horizontal"] {
-  margin-top: -10px;
-  min-height: 10px;
-  max-height: 10px;
-}
-
-*|*:not(html|select) > scrollbar thumb {
-  background-color: rgba(170, 170, 170, .2) !important; /* --toolbar-tab-hover */
-  -moz-appearance: none !important;
-  border-width: 0px !important;
-  border-radius: 3px !important;
-}
-
-*|*:root[platform="mac"] > scrollbar slider,
-*|*:root[platform="mac"] *|*:not(html|select) > scrollbar slider {
-  -moz-appearance: none !important;
-}
-
-*|*:root[platform="linux"] > scrollbar scrollbarbutton,
-*|*:root[platform="linux"] > scrollbar gripper,
-*|*:root[platform="linux"] *|*:not(html|select) > scrollbar scrollbarbutton,
-*|*:root[platform="linux"] *|*:not(html|select) > scrollbar gripper {
-  display: none;
-}