diff --git a/caps/nsIPrincipal.idl b/caps/nsIPrincipal.idl
index 51a896396086..abc7b9665ab9 100644
--- a/caps/nsIPrincipal.idl
+++ b/caps/nsIPrincipal.idl
@@ -308,22 +308,15 @@ interface nsIPrincipal : nsISerializable
     *
     * @param scheme    The scheme to be checked
     */
+    [infallible]
     boolean schemeIs(in string scheme);
 
-    // Nicer, C++ Callable Version of SchemeIs
-    %{C++
-      inline bool SchemeIs(const char* aScheme) {
-        bool ret;
-        SchemeIs(aScheme, &ret);
-        return ret;
-      }
-    %}
-
     /*
-    * Checks if the Principal's URI is contained in the given Pref
-    * @param pref    The pref to be checked
-    */
-    bool isURIInPrefList(in string pref);
+     * Checks if the Principal's URI is contained in the given Pref
+     * @param pref    The pref to be checked
+     */
+    [infallible]
+    boolean isURIInPrefList(in string pref);
 
     /*
     * Uses NS_Security Compare to determine if the
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index 40676dca7319..68d22f4f8170 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -8641,41 +8641,25 @@ nsresult PresShell::EventHandler::DispatchEventToDOM(
       // behave so, however, some web apps may be broken.  On such web apps,
       // we should keep using legacy our behavior.
       if (!mPresShell->mInitializedWithKeyPressEventDispatchingBlacklist) {
-        bool isInPrefList = false;
         mPresShell->mInitializedWithKeyPressEventDispatchingBlacklist = true;
         nsCOMPtr<nsIPrincipal> principal =
             GetDocumentPrincipalToCompareWithBlacklist(*mPresShell);
         if (principal) {
-          principal->IsURIInPrefList(
-              "dom.keyboardevent.keypress.hack.dispatch_non_printable_keys",
-              &isInPrefList);
           mPresShell->mForceDispatchKeyPressEventsForNonPrintableKeys =
-              isInPrefList;
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack.dispatch_non_printable_"
+                  "keys") ||
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "dispatch_non_printable_keys.addl");
 
-          principal->IsURIInPrefList(
-              "dom.keyboardevent.keypress.hack."
-              "dispatch_non_printable_keys.addl",
-              &isInPrefList);
-          mPresShell->mForceDispatchKeyPressEventsForNonPrintableKeys |=
-              isInPrefList;
-
-          principal->IsURIInPrefList(
-              "dom.keyboardevent.keypress.hack."
-              "use_legacy_keycode_and_charcode",
-              &isInPrefList);
-          mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |= isInPrefList;
-
-          principal->IsURIInPrefList(
-              "dom.keyboardevent.keypress.hack."
-              "use_legacy_keycode_and_charcode",
-              &isInPrefList);
-          mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |= isInPrefList;
-
-          principal->IsURIInPrefList(
-              "dom.keyboardevent.keypress.hack."
-              "use_legacy_keycode_and_charcode.addl",
-              &isInPrefList);
-          mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |= isInPrefList;
+          mPresShell->mForceUseLegacyKeyCodeAndCharCodeValues |=
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "use_legacy_keycode_and_charcode") ||
+              principal->IsURIInPrefList(
+                  "dom.keyboardevent.keypress.hack."
+                  "use_legacy_keycode_and_charcode.addl");
         }
       }
       if (mPresShell->mForceDispatchKeyPressEventsForNonPrintableKeys) {
@@ -8699,11 +8683,9 @@ nsresult PresShell::EventHandler::DispatchEventToDOM(
             GetDocumentPrincipalToCompareWithBlacklist(*mPresShell);
 
         if (principal) {
-          bool isInPrefList = false;
-          principal->IsURIInPrefList(
-              "dom.mouseevent.click.hack.use_legacy_non-primary_dispatch",
-              &isInPrefList);
-          mPresShell->mForceUseLegacyNonPrimaryDispatch = isInPrefList;
+          mPresShell->mForceUseLegacyNonPrimaryDispatch =
+              principal->IsURIInPrefList(
+                  "dom.mouseevent.click.hack.use_legacy_non-primary_dispatch");
         }
       }
       if (mPresShell->mForceUseLegacyNonPrimaryDispatch) {