Merge tag 'v1.6.0rc4' into sync/upstream-1.6.0rc4

Conflicts:
      app/javascript/mastodon/features/getting_started/index.js
      app/javascript/packs/public.js
      app/javascript/styles/components.scss

app/javascript/mastodon/features/ui/components/embed_modal.js

@@ -33,7 +33,8 @@ export default class EmbedModal extends ImmutablePureComponent {
       iframeDocument.close();
 
       iframeDocument.body.style.margin = 0;
-      this.iframe.height = iframeDocument.body.scrollHeight + 'px';
+      this.iframe.width  = iframeDocument.body.scrollWidth;
+      this.iframe.height = iframeDocument.body.scrollHeight;
     });
   }
 
@@ -71,7 +72,6 @@ export default class EmbedModal extends ImmutablePureComponent {
 
           <iframe
             className='embed-modal__iframe'
-            scrolling='no'
             frameBorder='0'
             ref={this.setIframeRef}
             title='preview'