I can not interact with an element inside the iframe

I can not interact with an element inside the iframe, adddon intalled.
I have the example in the page The Internet, I can’t to navigate into that iframe for example to Paragraph with contain “Your content goes here.”

The message in testproject is

THE TEST

-TestProject

MESSAGE

Failed to switch driver context to {{XPATH = //*[@id = ‘mce_0_ifr’]|/html/body/div[2]/div/div/div/div[1]/div[2]/div[1]/iframe

Element

Your content goes here.

Searched by XPATH://p

Please , I need help