Bug 1571567 - Fix no-fallthrough errors in /browser. r=MattN,k88hudson

Differential Revision: https://phabricator.services.mozilla.com/D40745

browser/components/preferences/in-content/main.js

@@ -3183,6 +3183,7 @@ class HandlerInfoWrapper {
         if (this instanceof InternalHandlerInfoWrapper) {
           return "ask";
         }
+        break;
 
       case kActionUsePlugin:
         return "plugin";
@@ -3201,10 +3202,10 @@ class HandlerInfoWrapper {
         if (gMainPane.isValidHandlerApp(preferredApp)) {
           return gMainPane._getIconURLForHandlerApp(preferredApp);
         }
-      // Explicit fall-through
 
       // This should never happen, but if preferredAction is set to some weird
       // value, then fall back to the generic application icon.
+      // Explicit fall-through
       default:
         return ICON_URL_APP;
     }