diff --git a/browser/modules/ExtensionsUI.jsm b/browser/modules/ExtensionsUI.jsm
index e51999c472de..1928f33cf333 100644
--- a/browser/modules/ExtensionsUI.jsm
+++ b/browser/modules/ExtensionsUI.jsm
@@ -16,8 +16,8 @@ XPCOMUtils.defineLazyModuleGetter(this, "AddonManagerPrivate",
                                   "resource://gre/modules/AddonManager.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "AppMenuNotifications",
                                   "resource://gre/modules/AppMenuNotifications.jsm");
-XPCOMUtils.defineLazyModuleGetter(this, "PluralForm",
-                                  "resource://gre/modules/PluralForm.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ExtensionData",
+                                  "resource://gre/modules/Extension.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "RecentWindow",
                                   "resource:///modules/RecentWindow.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
@@ -252,127 +252,15 @@ this.ExtensionsUI = {
 
   // Create a set of formatted strings for a permission prompt
   _buildStrings(info) {
-    let result = {};
-
     let bundle = Services.strings.createBundle(BROWSER_PROPERTIES);
 
-    let perms = info.permissions || {origins: [], permissions: []};
+    let brandBundle = Services.strings.createBundle(BRAND_PROPERTIES);
+    let appName = brandBundle.GetStringFromName("brandShortName");
+    let addonName = `<span class="addon-webext-name">${this._sanitizeName(info.addon.name)}</span>`;
 
-    // First classify our host permissions
-    let allUrls = false, wildcards = [], sites = [];
-    for (let permission of perms.origins) {
-      if (permission == "<all_urls>") {
-        allUrls = true;
-        break;
-      }
-      let match = /^[htps*]+:\/\/([^/]+)\//.exec(permission);
-      if (!match) {
-        Cu.reportError(`Unparseable host permission ${permission}`);
-        continue;
-      }
-      if (match[1] == "*") {
-        allUrls = true;
-      } else if (match[1].startsWith("*.")) {
-        wildcards.push(match[1].slice(2));
-      } else {
-        sites.push(match[1]);
-      }
-    }
+    let info2 = Object.assign({appName, addonName}, info);
 
-    // Format the host permissions.  If we have a wildcard for all urls,
-    // a single string will suffice.  Otherwise, show domain wildcards
-    // first, then individual host permissions.
-    result.msgs = [];
-    if (allUrls) {
-      result.msgs.push(bundle.GetStringFromName("webextPerms.hostDescription.allUrls"));
-    } else {
-      // Formats a list of host permissions.  If we have 4 or fewer, display
-      // them all, otherwise display the first 3 followed by an item that
-      // says "...plus N others"
-      function format(list, itemKey, moreKey) {
-        function formatItems(items) {
-          result.msgs.push(...items.map(item => bundle.formatStringFromName(itemKey, [item], 1)));
-        }
-        if (list.length < 5) {
-          formatItems(list);
-        } else {
-          formatItems(list.slice(0, 3));
-
-          let remaining = list.length - 3;
-          result.msgs.push(PluralForm.get(remaining, bundle.GetStringFromName(moreKey))
-                                     .replace("#1", remaining));
-        }
-      }
-
-      format(wildcards, "webextPerms.hostDescription.wildcard",
-             "webextPerms.hostDescription.tooManyWildcards");
-      format(sites, "webextPerms.hostDescription.oneSite",
-             "webextPerms.hostDescription.tooManySites");
-    }
-
-    let permissionKey = perm => `webextPerms.description.${perm}`;
-
-    // Next, show the native messaging permission if it is present.
-    const NATIVE_MSG_PERM = "nativeMessaging";
-    if (perms.permissions.includes(NATIVE_MSG_PERM)) {
-      let brandBundle = Services.strings.createBundle(BRAND_PROPERTIES);
-      let appName = brandBundle.GetStringFromName("brandShortName");
-      result.msgs.push(bundle.formatStringFromName(permissionKey(NATIVE_MSG_PERM), [appName], 1));
-    }
-
-    // Finally, show remaining permissions, in any order.
-    for (let permission of perms.permissions) {
-      // Handled above
-      if (permission == "nativeMessaging") {
-        continue;
-      }
-      try {
-        result.msgs.push(bundle.GetStringFromName(permissionKey(permission)));
-      } catch (err) {
-        // We deliberately do not include all permissions in the prompt.
-        // So if we don't find one then just skip it.
-      }
-    }
-
-    // Now figure out all the rest of the notification text.
-    let name = this._sanitizeName(info.addon.name);
-    let addonName = `<span class="addon-webext-name">${name}</span>`;
-
-    result.header = bundle.formatStringFromName("webextPerms.header", [addonName], 1);
-    result.text = info.unsigned ?
-                  bundle.GetStringFromName("webextPerms.unsignedWarning") : "";
-    result.listIntro = bundle.GetStringFromName("webextPerms.listIntro");
-
-    result.acceptText = bundle.GetStringFromName("webextPerms.add.label");
-    result.acceptKey = bundle.GetStringFromName("webextPerms.add.accessKey");
-    result.cancelText = bundle.GetStringFromName("webextPerms.cancel.label");
-    result.cancelKey = bundle.GetStringFromName("webextPerms.cancel.accessKey");
-
-    if (info.type == "sideload") {
-      result.header = bundle.formatStringFromName("webextPerms.sideloadHeader", [addonName], 1);
-      let key = result.msgs.length == 0 ?
-                "webextPerms.sideloadTextNoPerms" : "webextPerms.sideloadText2";
-      result.text = bundle.GetStringFromName(key);
-      result.acceptText = bundle.GetStringFromName("webextPerms.sideloadEnable.label");
-      result.acceptKey = bundle.GetStringFromName("webextPerms.sideloadEnable.accessKey");
-      result.cancelText = bundle.GetStringFromName("webextPerms.sideloadCancel.label");
-      result.cancelKey = bundle.GetStringFromName("webextPerms.sideloadCancel.accessKey");
-    } else if (info.type == "update") {
-      result.header = "";
-      result.text = bundle.formatStringFromName("webextPerms.updateText", [addonName], 1);
-      result.acceptText = bundle.GetStringFromName("webextPerms.updateAccept.label");
-      result.acceptKey = bundle.GetStringFromName("webextPerms.updateAccept.accessKey");
-    } else if (info.type == "optional") {
-      result.header = bundle.formatStringFromName("webextPerms.optionalPermsHeader", [addonName], 1);
-      result.text = "";
-      result.listIntro = bundle.GetStringFromName("webextPerms.optionalPermsListIntro");
-      result.acceptText = bundle.GetStringFromName("webextPerms.optionalPermsAllow.label");
-      result.acceptKey = bundle.GetStringFromName("webextPerms.optionalPermsAllow.accessKey");
-      result.cancelText = bundle.GetStringFromName("webextPerms.optionalPermsDeny.label");
-      result.cancelKey = bundle.GetStringFromName("webextPerms.optionalPermsDeny.accessKey");
-    }
-
-    return result;
+    return ExtensionData.formatPermissionStrings(info2, bundle);
   },
 
   showPermissionsPrompt(browser, strings, icon, histkey) {
diff --git a/toolkit/components/extensions/Extension.jsm b/toolkit/components/extensions/Extension.jsm
index d838d880141d..7505daae9024 100644
--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -57,6 +57,7 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   MessageChannel: "resource://gre/modules/MessageChannel.jsm",
   NetUtil: "resource://gre/modules/NetUtil.jsm",
   OS: "resource://gre/modules/osfile.jsm",
+  PluralForm: "resource://gre/modules/PluralForm.jsm",
   Schemas: "resource://gre/modules/Schemas.jsm",
   setTimeout: "resource://gre/modules/Timer.jsm",
   TelemetryStopwatch: "resource://gre/modules/TelemetryStopwatch.jsm",
@@ -790,6 +791,149 @@ this.ExtensionData = class {
     this.localeData.selectedLocale = locale;
     return results[0];
   }
+
+  /**
+   * Formats all the strings for a permissions dialog/notification.
+   *
+   * @param {object} info Information about the permissions being requested.
+   *
+   * @param {array<string>} info.permissions.origins
+   *                        Origin permissions requested.
+   * @param {array<string>} info.permissions.permissions
+   *                        Regular (non-origin) permissions requested.
+   * @param {AddonWrapper} info.addonName
+   *                       The name of the addon for which permissions are
+   *                       being requested.
+   * @param {boolean} info.unsigned
+   *                  True if the prompt is for installing an unsigned addon.
+   * @param {string} info.type
+   *                 The type of prompt being shown.  May be one of "update",
+   *                 "sideload", "optional", or omitted for a regular
+   *                 install prompt.
+   * @param {string} info.appName
+   *                 The localized name of the application, to be substituted
+   *                 in computed strings as needed.
+   * @param {nsIStringBundle} bundle
+   *                          The string bundle to use for l10n.
+   *
+   * @returns {object} An object with properties containing localized strings
+   *                   for various elements of a permission dialog.
+   */
+  static formatPermissionStrings(info, bundle) {
+    let result = {};
+
+    let perms = info.permissions || {origins: [], permissions: []};
+
+    // First classify our host permissions
+    let allUrls = false, wildcards = [], sites = [];
+    for (let permission of perms.origins) {
+      if (permission == "<all_urls>") {
+        allUrls = true;
+        break;
+      }
+      let match = /^[htps*]+:\/\/([^/]+)\//.exec(permission);
+      if (!match) {
+        Cu.reportError(`Unparseable host permission ${permission}`);
+        continue;
+      }
+      if (match[1] == "*") {
+        allUrls = true;
+      } else if (match[1].startsWith("*.")) {
+        wildcards.push(match[1].slice(2));
+      } else {
+        sites.push(match[1]);
+      }
+    }
+
+    // Format the host permissions.  If we have a wildcard for all urls,
+    // a single string will suffice.  Otherwise, show domain wildcards
+    // first, then individual host permissions.
+    result.msgs = [];
+    if (allUrls) {
+      result.msgs.push(bundle.GetStringFromName("webextPerms.hostDescription.allUrls"));
+    } else {
+      // Formats a list of host permissions.  If we have 4 or fewer, display
+      // them all, otherwise display the first 3 followed by an item that
+      // says "...plus N others"
+      let format = (list, itemKey, moreKey) => {
+        function formatItems(items) {
+          result.msgs.push(...items.map(item => bundle.formatStringFromName(itemKey, [item], 1)));
+        }
+        if (list.length < 5) {
+          formatItems(list);
+        } else {
+          formatItems(list.slice(0, 3));
+
+          let remaining = list.length - 3;
+          result.msgs.push(PluralForm.get(remaining, bundle.GetStringFromName(moreKey))
+                                     .replace("#1", remaining));
+        }
+      };
+
+      format(wildcards, "webextPerms.hostDescription.wildcard",
+             "webextPerms.hostDescription.tooManyWildcards");
+      format(sites, "webextPerms.hostDescription.oneSite",
+             "webextPerms.hostDescription.tooManySites");
+    }
+
+    let permissionKey = perm => `webextPerms.description.${perm}`;
+
+    // Next, show the native messaging permission if it is present.
+    const NATIVE_MSG_PERM = "nativeMessaging";
+    if (perms.permissions.includes(NATIVE_MSG_PERM)) {
+      result.msgs.push(bundle.formatStringFromName(permissionKey(NATIVE_MSG_PERM), [info.appName], 1));
+    }
+
+    // Finally, show remaining permissions, in any order.
+    for (let permission of perms.permissions) {
+      // Handled above
+      if (permission == "nativeMessaging") {
+        continue;
+      }
+      try {
+        result.msgs.push(bundle.GetStringFromName(permissionKey(permission)));
+      } catch (err) {
+        // We deliberately do not include all permissions in the prompt.
+        // So if we don't find one then just skip it.
+      }
+    }
+
+    result.header = bundle.formatStringFromName("webextPerms.header", [info.addonName], 1);
+    result.text = info.unsigned ?
+                  bundle.GetStringFromName("webextPerms.unsignedWarning") : "";
+    result.listIntro = bundle.GetStringFromName("webextPerms.listIntro");
+
+    result.acceptText = bundle.GetStringFromName("webextPerms.add.label");
+    result.acceptKey = bundle.GetStringFromName("webextPerms.add.accessKey");
+    result.cancelText = bundle.GetStringFromName("webextPerms.cancel.label");
+    result.cancelKey = bundle.GetStringFromName("webextPerms.cancel.accessKey");
+
+    if (info.type == "sideload") {
+      result.header = bundle.formatStringFromName("webextPerms.sideloadHeader", [info.addonName], 1);
+      let key = result.msgs.length == 0 ?
+                "webextPerms.sideloadTextNoPerms" : "webextPerms.sideloadText2";
+      result.text = bundle.GetStringFromName(key);
+      result.acceptText = bundle.GetStringFromName("webextPerms.sideloadEnable.label");
+      result.acceptKey = bundle.GetStringFromName("webextPerms.sideloadEnable.accessKey");
+      result.cancelText = bundle.GetStringFromName("webextPerms.sideloadCancel.label");
+      result.cancelKey = bundle.GetStringFromName("webextPerms.sideloadCancel.accessKey");
+    } else if (info.type == "update") {
+      result.header = "";
+      result.text = bundle.formatStringFromName("webextPerms.updateText", [info.addonName], 1);
+      result.acceptText = bundle.GetStringFromName("webextPerms.updateAccept.label");
+      result.acceptKey = bundle.GetStringFromName("webextPerms.updateAccept.accessKey");
+    } else if (info.type == "optional") {
+      result.header = bundle.formatStringFromName("webextPerms.optionalPermsHeader", [info.addonName], 1);
+      result.text = "";
+      result.listIntro = bundle.GetStringFromName("webextPerms.optionalPermsListIntro");
+      result.acceptText = bundle.GetStringFromName("webextPerms.optionalPermsAllow.label");
+      result.acceptKey = bundle.GetStringFromName("webextPerms.optionalPermsAllow.accessKey");
+      result.cancelText = bundle.GetStringFromName("webextPerms.optionalPermsDeny.label");
+      result.cancelKey = bundle.GetStringFromName("webextPerms.optionalPermsDeny.accessKey");
+    }
+
+    return result;
+  }
 };
 
 const PROXIED_EVENTS = new Set(["test-harness-message", "add-permissions", "remove-permissions"]);