- l10n: Add Chinese (simplified) extension locales (Thanks, @enlove!)

- Linting (ESLint): Avoid reporting `no-console`
- Refactoring: Avoid Firefox console errors with hidden iframe
- Docs (CHANGES): Fix Markdown heading level

.eslintrc.js

@@ -144,6 +144,7 @@ module.exports = {
     complexity: ["off"],
     "default-case": ["off"],
     "require-unicode-regexp": ["off"],
+    "no-console": ["off"],
     "no-magic-numbers": ["off"],
     "no-warning-comments": ["off"],
     "max-len": ["off", {