Possible CSS Bug in FF

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS @property Cross-Browser Fix</title>

    <style>
        @property --im-a-color {
            syntax: "<color>";
            inherits: false;
            initial-value: red;
        }

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

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

        /* Default heading color */
        h1 {
            color: black;
        }

        /* Explicitly match blue instead of using
           a boolean custom property style query */
        @container style(--im-a-color: blue) {
            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>

    <script>
        document.querySelectorAll("body > div").forEach((div, index) => {
            const heading = div.querySelector("h1");

            console.log({
                heading: index + 1,
                className: div.className || "(none)",
                customProperty: getComputedStyle(div)
                    .getPropertyValue("--im-a-color")
                    .trim(),
                headingColor: getComputedStyle(heading).color
            });
        });
    </script>
</body>
</html>