diff --git a/toolkit/components/telemetry/TelemetryEnvironment.jsm b/toolkit/components/telemetry/TelemetryEnvironment.jsm
index eddffb699de..8706ef1f964 100644
--- a/toolkit/components/telemetry/TelemetryEnvironment.jsm
+++ b/toolkit/components/telemetry/TelemetryEnvironment.jsm
@@ -1259,7 +1259,8 @@ EnvironmentCache.prototype = {
         // Query the UBR key and only add it to the environment if it's available.
         // |readRegKey| doesn't throw, but rather returns 'undefined' on error.
         let ubr = WindowsRegistry.readRegKey(Ci.nsIWindowsRegKey.ROOT_KEY_LOCAL_MACHINE,
-                                             WINDOWS_UBR_KEY_PATH, "UBR");
+                                             WINDOWS_UBR_KEY_PATH, "UBR",
+                                             Ci.nsIWindowsRegKey.WOW64_64);
         data.windowsUBR = (ubr !== undefined) ? ubr : null;
       }
       data.installYear = getSysinfoProperty("installYear", null);
diff --git a/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js b/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js
index dc2908956bf..6c43fc55fd5 100644
--- a/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryEnvironment.js
@@ -518,8 +518,8 @@ function checkSystemSection(data) {
     }
     if ("windowsUBR" in osData) {
       // This might not be available on all Windows platforms.
-      Assert.ok(Number.isFinite(osData["windowsUBR"]),
-                "windowsUBR must be a number.");
+      Assert.ok((osData["windowsUBR"] === null) || Number.isFinite(osData["windowsUBR"]),
+                "windowsUBR must be null or a number.");
     }
   } else if (gIsAndroid || gIsGonk) {
     Assert.ok(checkNullOrString(osData.kernelVersion));
diff --git a/toolkit/modules/WindowsRegistry.jsm b/toolkit/modules/WindowsRegistry.jsm
index 2e7a5ad3938..c015d1eefcb 100644
--- a/toolkit/modules/WindowsRegistry.jsm
+++ b/toolkit/modules/WindowsRegistry.jsm
@@ -17,15 +17,19 @@ var WindowsRegistry = {
    *        The registry path to the key.
    * @param aKey
    *        The key name.
+   * @param [aRegistryNode=0]
+   *        Optionally set to nsIWindowsRegKey.WOW64_64 (or nsIWindowsRegKey.WOW64_32)
+   *        to access a 64-bit (32-bit) key from either a 32-bit or 64-bit application.
    * @return The key value or undefined if it doesn't exist.  If the key is
    *         a REG_MULTI_SZ, an array is returned.
    */
-  readRegKey: function(aRoot, aPath, aKey) {
+  readRegKey: function(aRoot, aPath, aKey, aRegistryNode=0) {
     const kRegMultiSz = 7;
+    const kMode = Ci.nsIWindowsRegKey.ACCESS_READ | aRegistryNode;
     let registry = Cc["@mozilla.org/windows-registry-key;1"].
                    createInstance(Ci.nsIWindowsRegKey);
     try {
-      registry.open(aRoot, aPath, Ci.nsIWindowsRegKey.ACCESS_READ);
+      registry.open(aRoot, aPath, kMode);
       if (registry.hasValue(aKey)) {
         let type = registry.getValueType(aKey);
         switch (type) {
@@ -57,13 +61,17 @@ var WindowsRegistry = {
    *        The registry path to the key.
    * @param aKey
    *        The key name.
+   * @param [aRegistryNode=0]
+   *        Optionally set to nsIWindowsRegKey.WOW64_64 (or nsIWindowsRegKey.WOW64_32)
+   *        to access a 64-bit (32-bit) key from either a 32-bit or 64-bit application.
    */
-  removeRegKey: function(aRoot, aPath, aKey) {
+  removeRegKey: function(aRoot, aPath, aKey, aRegistryNode=0) {
     let registry = Cc["@mozilla.org/windows-registry-key;1"].
                    createInstance(Ci.nsIWindowsRegKey);
     try {
       let mode = Ci.nsIWindowsRegKey.ACCESS_QUERY_VALUE |
-                 Ci.nsIWindowsRegKey.ACCESS_SET_VALUE;
+                 Ci.nsIWindowsRegKey.ACCESS_SET_VALUE |
+                 aRegistryNode;
       registry.open(aRoot, aPath, mode);
       if (registry.hasValue(aKey)) {
         registry.removeValue(aKey);