diff --git a/toolkit/components/extensions/ext-browserSettings.js b/toolkit/components/extensions/ext-browserSettings.js
index 5efaef086ab8..e7d45e25b63d 100644
--- a/toolkit/components/extensions/ext-browserSettings.js
+++ b/toolkit/components/extensions/ext-browserSettings.js
@@ -2,8 +2,6 @@
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
-XPCOMUtils.defineLazyModuleGetter(this, "AppConstants",
-                                  "resource://gre/modules/AppConstants.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
                                   "resource://gre/modules/Services.jsm");
 
@@ -13,10 +11,6 @@ XPCOMUtils.defineLazyServiceGetter(this, "aboutNewTabService",
 
 Cu.import("resource://gre/modules/ExtensionPreferencesManager.jsm");
 
-var {
-  ExtensionError,
-} = ExtensionUtils;
-
 const HOMEPAGE_OVERRIDE_SETTING = "homepage_override";
 const HOMEPAGE_URL_PREF = "browser.startup.homepage";
 const URL_STORE_TYPE = "url_overrides";
@@ -88,16 +82,6 @@ ExtensionPreferencesManager.addSetting("imageAnimationBehavior", {
   },
 });
 
-ExtensionPreferencesManager.addSetting("contextMenuShowEvent", {
-  prefNames: [
-    "ui.context_menus.after_mouseup",
-  ],
-
-  setCallback(value) {
-    return {[this.prefNames[0]]: value === "mouseup"};
-  },
-});
-
 ExtensionPreferencesManager.addSetting("webNotificationsDisabled", {
   prefNames: [
     "permissions.default.desktop-notification",
@@ -140,35 +124,6 @@ this.browserSettings = class extends ExtensionAPI {
           () => {
             return aboutNewTabService.newTabURL;
           }, URL_STORE_TYPE, true),
-        contextMenuShowEvent: Object.assign(
-          getSettingsAPI(
-            extension,
-            "contextMenuShowEvent",
-            () => {
-              if (AppConstants.platform === "win") {
-                return "mouseup";
-              }
-              let prefValue = Services.prefs.getBoolPref(
-                "ui.context_menus.after_mouseup", null);
-              return prefValue ? "mouseup" : "mousedown";
-            }
-          ),
-          {
-            set: details => {
-              if (!["mouseup", "mousedown"].includes(details.value)) {
-                throw new ExtensionError(
-                  `${details.value} is not a valid value for contextMenuShowEvent.`);
-              }
-              if (AppConstants.platform === "android" ||
-                  (AppConstants.platform === "win" &&
-                   details.value === "mousedown")) {
-                return false;
-              }
-              return ExtensionPreferencesManager.setSetting(
-                extension.id, "contextMenuShowEvent", details.value);
-            },
-          }
-        ),
         webNotificationsDisabled: getSettingsAPI(extension,
           "webNotificationsDisabled",
           () => {
diff --git a/toolkit/components/extensions/schemas/browser_settings.json b/toolkit/components/extensions/schemas/browser_settings.json
index 791240a1865a..adf4ef4c163c 100644
--- a/toolkit/components/extensions/schemas/browser_settings.json
+++ b/toolkit/components/extensions/schemas/browser_settings.json
@@ -27,12 +27,6 @@
         "type": "string",
         "enum": ["normal", "none", "once"],
         "description": "How images should be animated in the browser."
-      },
-      {
-        "id": "ContextMenuMouseEvent",
-        "type": "string",
-        "enum": ["mouseup", "mousedown"],
-        "description": "After which mouse event context menus should popup."
       }
     ],
     "properties": {
@@ -56,10 +50,6 @@
         "$ref": "types.Setting",
         "description": "Returns the value of the overridden new tab page. Read-only."
       },
-      "contextMenuShowEvent": {
-        "$ref": "types.Setting",
-        "description": "Controls after which mouse event context menus popup. This setting's value is of type ContextMenuMouseEvent, which has possible values of <code>mouseup</code> and <code>mousedown</code>."
-      },
       "webNotificationsDisabled": {
         "$ref": "types.Setting",
         "description": "Disables webAPI notifications."
diff --git a/toolkit/components/extensions/test/xpcshell/test_ext_browserSettings.js b/toolkit/components/extensions/test/xpcshell/test_ext_browserSettings.js
index 08ba62e6dc5a..b2e3b4d01e4a 100644
--- a/toolkit/components/extensions/test/xpcshell/test_ext_browserSettings.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_browserSettings.js
@@ -28,20 +28,13 @@ add_task(async function test_browser_settings() {
     "dom.popup_allowed_events": Preferences.get("dom.popup_allowed_events"),
     "image.animation_mode": "none",
     "permissions.default.desktop-notification": PERM_UNKNOWN_ACTION,
-    "ui.context_menus.after_mouseup": false,
   };
 
   async function background() {
     browser.test.onMessage.addListener(async (msg, apiName, value) => {
       let apiObj = browser.browserSettings[apiName];
-      let result = await apiObj.set({value});
-      if (msg === "set") {
-        browser.test.assertTrue(result, "set returns true.");
-        browser.test.sendMessage("settingData", await apiObj.get({}));
-      } else {
-        browser.test.assertFalse(result, "set returns false for a no-op.");
-        browser.test.sendMessage("no-op set");
-      }
+      await apiObj.set({value});
+      browser.test.sendMessage("settingData", await apiObj.get({}));
     });
   }
 
@@ -80,14 +73,6 @@ add_task(async function test_browser_settings() {
     }
   }
 
-  async function testNoOpSetting(setting, value, expected) {
-    extension.sendMessage("setNoOp", setting, value);
-    await extension.awaitMessage("no-op set");
-    for (let pref in expected) {
-      equal(Preferences.get(pref), expected[pref], `${pref} set correctly for ${value}`);
-    }
-  }
-
   await testSetting(
     "cacheEnabled", false,
     {
@@ -125,48 +110,7 @@ add_task(async function test_browser_settings() {
         AppConstants.MOZ_BUILD_APP !== "browser" ? undefined : PERM_UNKNOWN_ACTION,
     });
 
-  // This setting is a no-op on Android.
-  if (AppConstants.platform === "android") {
-    await testNoOpSetting("contextMenuShowEvent", "mouseup",
-      {"ui.context_menus.after_mouseup": false});
-  } else {
-    await testSetting(
-      "contextMenuShowEvent", "mouseup",
-      {"ui.context_menus.after_mouseup": true});
-  }
-
-  // "mousedown" is also a no-op on Windows.
-  if (["android", "win"].includes(AppConstants.platform)) {
-    await testNoOpSetting("contextMenuShowEvent", "mousedown",
-      {"ui.context_menus.after_mouseup": false});
-  } else {
-    await testSetting(
-      "contextMenuShowEvent", "mousedown",
-      {"ui.context_menus.after_mouseup": false});
-  }
-
   await extension.unload();
+
   await promiseShutdownManager();
 });
-
-add_task(async function test_bad_value() {
-  async function background() {
-    await browser.test.assertRejects(
-      browser.browserSettings.contextMenuShowEvent.set({value: "bad"}),
-      /bad is not a valid value for contextMenuShowEvent/,
-      "contextMenuShowEvent.set rejects with an invalid value.");
-
-    browser.test.sendMessage("done");
-  }
-
-  let extension = ExtensionTestUtils.loadExtension({
-    background,
-    manifest: {
-      permissions: ["browserSettings"],
-    },
-  });
-
-  await extension.startup();
-  await extension.awaitMessage("done");
-  await extension.unload();
-});