--- a/toolkit/mozapps/extensions/content/extensions.js
+++ b/toolkit/mozapps/extensions/content/extensions.js
@@ -43,16 +43,19 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 XPCOMUtils.defineLazyModuleGetter(this, "Experiments",
   "resource:///modules/experiments/Experiments.jsm");
 
 XPCOMUtils.defineLazyPreferenceGetter(this, "WEBEXT_PERMISSION_PROMPTS",
                                       "extensions.webextPermissionPrompts", false);
 XPCOMUtils.defineLazyPreferenceGetter(this, "ALLOW_NON_MPC",
                                       "extensions.allow-non-mpc-extensions", true);
 
+XPCOMUtils.defineLazyPreferenceGetter(this, "SUPPORT_URL", "app.support.baseURL",
+                                      "", null, val => Services.urlFormatter.formatURL(val));
+
 const PREF_DISCOVERURL = "extensions.webservice.discoverURL";
 const PREF_DISCOVER_ENABLED = "extensions.getAddons.showPane";
 const PREF_XPI_ENABLED = "xpinstall.enabled";
 const PREF_MAXRESULTS = "extensions.getAddons.maxResults";
 const PREF_GETADDONS_CACHE_ENABLED = "extensions.getAddons.cache.enabled";
 const PREF_GETADDONS_CACHE_ID_ENABLED = "extensions.%ID%.getAddons.cache.enabled";
 const PREF_UI_TYPE_HIDDEN = "extensions.ui.%TYPE%.hidden";
 const PREF_UI_LASTCATEGORY = "extensions.ui.lastCategory";
@@ -2821,18 +2824,17 @@ var gListView = {
     this._listBox.addEventListener("keydown", (aEvent) => {
       if (aEvent.keyCode == aEvent.DOM_VK_RETURN) {
         var item = this._listBox.selectedItem;
         if (item)
           item.showInDetailView();
       }
     });
 
-    document.getElementById("signing-learn-more").setAttribute("href",
-      Services.urlFormatter.formatURLPref("app.support.baseURL") + "unsigned-addons");
+    document.getElementById("signing-learn-more").setAttribute("href", SUPPORT_URL + "unsigned-addons");
 
     let findSignedAddonsLink = document.getElementById("find-alternative-addons");
     try {
       findSignedAddonsLink.setAttribute("href",
         Services.urlFormatter.formatURLPref("extensions.getAddons.link.url"));
     } catch (e) {
       findSignedAddonsLink.classList.remove("text-link");
     }
@@ -2841,17 +2843,17 @@ var gListView = {
       document.getElementById("signing-dev-manual-link").setAttribute("href",
         Services.prefs.getCharPref("xpinstall.signatures.devInfoURL"));
     } catch (e) {
       document.getElementById("signing-dev-info").hidden = true;
     }
 
     if (Preferences.get("plugin.load_flash_only", true)) {
       document.getElementById("plugindeprecation-learnmore-link")
-        .setAttribute("href", Services.urlFormatter.formatURLPref("app.support.baseURL") + "npapi");
+        .setAttribute("href", SUPPORT_URL + "npapi");
     } else {
       document.getElementById("plugindeprecation-notice").hidden = true;
     }
 
     if (Preferences.get("extensions.getAddons.themes.browseURL", "")) {
       document.getElementById("getthemes-learnmore-link")
         .setAttribute("href", Services.urlFormatter.formatURLPref("extensions.getAddons.themes.browseURL"));
     } else {
@@ -3396,17 +3398,17 @@ var gDetailView = {
         errorLink.hidden = false;
       } else if (!isCorrectlySigned(this._addon) && SIGNING_REQUIRED) {
         this.node.setAttribute("notification", "error");
         document.getElementById("detail-error").textContent = gStrings.ext.formatStringFromName(
           "details.notification.unsignedAndDisabled", [this._addon.name, gStrings.brandShortName], 2
         );
         let errorLink = document.getElementById("detail-error-link");
         errorLink.value = gStrings.ext.GetStringFromName("details.notification.unsigned.link");
-        errorLink.href = Services.urlFormatter.formatURLPref("app.support.baseURL") + "unsigned-addons";
+        errorLink.href = SUPPORT_URL + "unsigned-addons";
         errorLink.hidden = false;
       } else if (!this._addon.isCompatible && (AddonManager.checkCompatibility ||
         (this._addon.blocklistState != Ci.nsIBlocklistService.STATE_SOFTBLOCKED))) {
         this.node.setAttribute("notification", "warning");
         document.getElementById("detail-warning").textContent = gStrings.ext.formatStringFromName(
           "details.notification.incompatible",
           [this._addon.name, gStrings.brandShortName, gStrings.appVersion], 3
         );
@@ -3421,17 +3423,17 @@ var gDetailView = {
         errorLink.href = "https://wiki.mozilla.org/Add-ons/ShimsNightly";
       } else if (!isCorrectlySigned(this._addon)) {
         this.node.setAttribute("notification", "warning");
         document.getElementById("detail-warning").textContent = gStrings.ext.formatStringFromName(
           "details.notification.unsigned", [this._addon.name, gStrings.brandShortName], 2
         );
         var warningLink = document.getElementById("detail-warning-link");
         warningLink.value = gStrings.ext.GetStringFromName("details.notification.unsigned.link");
-        warningLink.href = Services.urlFormatter.formatURLPref("app.support.baseURL") + "unsigned-addons";
+        warningLink.href = SUPPORT_URL + "unsigned-addons";
         warningLink.hidden = false;
       } else if (this._addon.blocklistState == Ci.nsIBlocklistService.STATE_SOFTBLOCKED) {
         this.node.setAttribute("notification", "warning");
         document.getElementById("detail-warning").textContent = gStrings.ext.formatStringFromName(
           "details.notification.softblocked",
           [this._addon.name], 1
         );
         let warningLink = document.getElementById("detail-warning-link");

--- a/toolkit/mozapps/extensions/content/extensions.xml
+++ b/toolkit/mozapps/extensions/content/extensions.xml
@@ -1302,17 +1302,17 @@
               this._errorLink.href = this.mAddon.blocklistURL;
               this._errorLink.hidden = false;
             } else if (!isUpgrade && !isCorrectlySigned(this.mAddon) && SIGNING_REQUIRED) {
               this.setAttribute("notification", "error");
               this._error.textContent = gStrings.ext.formatStringFromName(
                 "notification.unsignedAndDisabled", [this.mAddon.name, gStrings.brandShortName], 2
               );
               this._errorLink.value = gStrings.ext.GetStringFromName("notification.unsigned.link");
-              this._errorLink.href = Services.urlFormatter.formatURLPref("app.support.baseURL") + "unsigned-addons";
+              this._errorLink.href = SUPPORT_URL + "unsigned-addons";
               this._errorLink.hidden = false;
             } else if ((!isUpgrade && !this.mAddon.isCompatible) && (AddonManager.checkCompatibility
             || (this.mAddon.blocklistState != Ci.nsIBlocklistService.STATE_SOFTBLOCKED))) {
               this.setAttribute("notification", "warning");
               this._warning.textContent = gStrings.ext.formatStringFromName(
                 "notification.incompatible",
                 [this.mAddon.name, gStrings.brandShortName, gStrings.appVersion], 3
               );
@@ -1329,17 +1329,17 @@
               this._errorLink.href = "https://wiki.mozilla.org/Add-ons/ShimsNightly";
               this._errorLink.hidden = false;
             } else if (!isUpgrade && !isCorrectlySigned(this.mAddon)) {
               this.setAttribute("notification", "warning");
               this._warning.textContent = gStrings.ext.formatStringFromName(
                 "notification.unsigned", [this.mAddon.name, gStrings.brandShortName], 2
               );
               this._warningLink.value = gStrings.ext.GetStringFromName("notification.unsigned.link");
-              this._warningLink.href = Services.urlFormatter.formatURLPref("app.support.baseURL") + "unsigned-addons";
+              this._warningLink.href = SUPPORT_URL + "unsigned-addons";
               this._warningLink.hidden = false;
             } else if (!isUpgrade && this.mAddon.blocklistState == Ci.nsIBlocklistService.STATE_SOFTBLOCKED) {
               this.setAttribute("notification", "warning");
               this._warning.textContent = gStrings.ext.formatStringFromName(
                 "notification.softblocked",
                 [this.mAddon.name], 1
               );
               this._warningLink.value = gStrings.ext.GetStringFromName("notification.softblocked.link");