Joomla! Documentation™

When you are inserting images or page break (on tinyMCE), the location of the item you added is on beginning position of the article and not the original location when the mouse cursor was before press the button.

For fixing this issue, you'll require to add the next css code to the end of the file media/system/css/modal.css:

@-moz-document url-prefix() {
    .body-overlayed {
	overflow: visible;
    }
}