What you needs to do?

The Matrix Object namespaced is defined as window.fu_matrix, which you needs to be hardcoded into your website pages tag. Variables within these variable shod be populated dynamically as per the page(e.g. user details, page detail, product details, etc.). So your page is look similar to below:

<head>
 <!-- Other Code -->
<script type="text/javascript">
    window.fu_matrix = {
        // Add your variables here
    };
</script>
</head>

Structure

As we stated before that Frontuser Matrix object is flexible around all businesses, there is no restriction to add specific variables. However, it only contains valid JSON string.

Recommended

Validate your JSON string at JSONLint or JSON Validator tool before add your variables.