captcha not working with FF55.0.3

Firefox seems to have some problems with captcha.

According to the following website, there seems to be a coding issue on the XN website that is subject to that glitch.

Copied from https://contactform7.com/faq/captcha-s-text-input-box-is-working-on-inte...

 <blockquote>

This is a well-known issue caused by misusing the <label> element. Make sure you are using it correctly. 

This is good:

[captchac your-captcha]
<label>Enter the code: [captchar your-captcha]</label>

This will not work correctly:

<label>[captchac your-captcha]
Enter the code: [captchar your-captcha]</label>



 </blockquote>