diff --git a/caps/src/nsScriptSecurityManager.cpp b/caps/src/nsScriptSecurityManager.cpp
index ed2df23dd97..700210fbbdc 100644
--- a/caps/src/nsScriptSecurityManager.cpp
+++ b/caps/src/nsScriptSecurityManager.cpp
@@ -2799,7 +2799,9 @@ nsScriptSecurityManager::RequestCapability(nsIPrincipal* aPrincipal,
     {
         // Prompt user for permission to enable capability.
         JSContext* cx = GetCurrentJSContext();
-        PRBool remember;
+        // The actual value is irrelevant but we shouldn't be handing out
+        // malformed JSBools to XPConnect.
+        PRBool remember = PR_FALSE;
         if (CheckConfirmDialog(cx, aPrincipal, capability, &remember))
             *canEnable = nsIPrincipal::ENABLE_GRANTED;
         else
diff --git a/netwerk/protocol/http/nsHttpChannelAuthProvider.cpp b/netwerk/protocol/http/nsHttpChannelAuthProvider.cpp
index a4e1f4d94d2..c23c6858b52 100644
--- a/netwerk/protocol/http/nsHttpChannelAuthProvider.cpp
+++ b/netwerk/protocol/http/nsHttpChannelAuthProvider.cpp
@@ -1182,7 +1182,9 @@ nsHttpChannelAuthProvider::ConfirmAuth(const nsString &bundleKey,
     PRBool confirmed;
     if (doYesNoPrompt) {
         PRInt32 choice;
-        PRBool checkState;
+        // The actual value is irrelevant but we shouldn't be handing out
+        // malformed JSBools to XPConnect.
+        PRBool checkState = PR_FALSE;
         rv = prompt->ConfirmEx(nsnull, msg,
                                nsIPrompt::BUTTON_POS_1_DEFAULT +
                                nsIPrompt::STD_YES_NO_BUTTONS,
diff --git a/security/manager/ssl/src/nsCrypto.cpp b/security/manager/ssl/src/nsCrypto.cpp
index 91637bf51bd..9fe741fb868 100644
--- a/security/manager/ssl/src/nsCrypto.cpp
+++ b/security/manager/ssl/src/nsCrypto.cpp
@@ -2937,7 +2937,9 @@ confirm_user(const PRUnichar *message)
   if (prompter) {
     nsPSMUITracker tracker;
     if (!tracker.isUIForbidden()) {
-      PRBool checkState;
+      // The actual value is irrelevant but we shouldn't be handing out
+      // malformed JSBools to XPConnect.
+      PRBool checkState = PR_FALSE;
       prompter->ConfirmEx(0, message,
                           (nsIPrompt::BUTTON_DELAY_ENABLE) +
                           (nsIPrompt::BUTTON_POS_1_DEFAULT) +
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index ccc99d1785f..bff04c5887f 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -1809,7 +1809,9 @@ ProfileLockedDialog(nsILocalFile* aProfileDir, nsILocalFile* aProfileLocalDir,
     }
 
     PRInt32 button;
-    PRBool checkState;
+    // The actual value is irrelevant but we shouldn't be handing out
+    // malformed JSBools to XPConnect.
+    PRBool checkState = PR_FALSE;
     rv = ps->ConfirmEx(nsnull, killTitle, killMessage, flags,
                        killTitle, nsnull, nsnull, nsnull, &checkState, &button);
     NS_ENSURE_SUCCESS_LOG(rv, rv);