- 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

editor/extensions/ext-server_opensave.js

@@ -59,7 +59,9 @@ export default {
 
     let cancelled = false;
 
-    $('<iframe name="output_frame" src="#"/>').hide().appendTo('body');
+    //  Hiding by size instead of display to avoid FF console errors
+    //    with `getBBox` in browser.js `supportsPathBBox_`)
+    $('<iframe name="output_frame" style="width: 0; height: 0;" src="#"/>').appendTo('body');
     svgEditor.setCustomHandlers({
       save (win, data) {
         const svg = '<?xml version="1.0" encoding="UTF-8"?>\n' + data, // Firefox doesn't seem to know it is UTF-8 (no matter whether we use or skip the clientDownload code) despite the Content-Disposition header containing UTF-8, but adding the encoding works