Possible CSS Bug in FF

HTML

<!DOCTYPE html>
<html>
    <head>
        <title>Minimal sample</title>
        <style>
            @property --im-a-color {
                syntax: "<color>";
                inherits: false;
                initial-value: red;
            }
            
            .red {
                --im-a-color: red;
            }

            .blue {
                --im-a-color: blue;
            }

            @container style(--im-a-color) {
                h1 {
                    color: green;
                }
            }
        </style>
    </head>
    <body>
        <div>
            <h1>I should be black</h1>
        </div>
        <div class="red">
            <h1>I should also be black</h1>
        </div>
        <div class="blue">
            <h1>I should be green</h1>
        </div>
    </body>
</html>