The share option of a video generates an iframe code snippet with numerous options. You can adjust the size manually if needed.
If you see a message such as "Firefox can't open this page in a frame", this is usually caused by a CORS restriction on your web server. On WordPress, add the following to your .htaccess file:
<IfModule mod_headers.c>
header set X-Frame-Options "allow-from https://fair.tube"
</IfModule>