Ignore X-Frame-Options Firefox extension:

This extension allows you to load remote content in iframes even if the server disallow framing

Here is a page designed for testing
https://www.w3schools.com/code/tryit.asp?filename=GEFNSY7F440P

Install

• License: Mozilla Public License 2.0
• Weekly downloads: 117
• Average daily users: 9168
• Rating: 4.5098/5 of 51 ratings
• Created: 2018-07-16 15:42:33
• Last updated: 2020-08-01 17:10:15
• Homepage: https://github.com/ThomazPom/Moz-Ext-Ignore-X-Frame-Options
• Support site and email
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• Orig: https://addons.mozilla.org/en-US/firefox/addon/ignore-x-frame-options-header/
• API: {a6afa2be-9b78-4dba-9dda-d89e52b13b7d}