Standard page resizes or flickers for a short time when it loads if the page has embedded Visualforce page component

Problem Description

When a Salesforce standard page layout contains an embedded Visualforce page component, the standard page may flicker or briefly resize during loading in the Google Chrome browser.

Root Cause

This behavior is a Chrome browser rendering issue related to cross-domain iframe CSS initialization — it is not a Salesforce platform defect. The flickering occurs because the embedded Visualforce page initializes its own CSS Style section, which triggers a cross-domain iframe resize event that the parent standard page reacts to visually.

Conditions Required to Reproduce

All of the following conditions must be met for the issue to reproduce:

1. Google Chrome browser
2. Windows 7 or Windows 10
3. External monitor connected to the laptop via HDMI
4. Different display scaling settings configured on the native and external monitors

Why This Also Occurs Outside Salesforce

The same rendering behavior can be reproduced in Chrome outside of Salesforce under the following cross-domain iframe conditions:

• The main page is served from Domain A
• The main page has iframe elements as embedded content
• The content of the iframe elements is served from Domain B
• The content within the iframe has a nested iframe element
• The nested iframe content is served back from Domain A

This circular cross-domain iframe reference triggers the CSS initialization and resize behavior in Chrome.