tinymce-docs-4x/_includes/configuration/relative-urls.md

relative_urls

If this option is set to true, all URLs returned from the MCFileManager will be relative from the specified document_base_url. If it's set to false all URLs will be converted to absolute URLs.

Type: Boolean

Default Value: true

Possible Values: true, false

Example:

tinymce.init({
  selector: "textarea",  // change this value according to your html
  relative_urls: false
});