diff --git a/tests/test.h264.js b/tests/test.h264.js
index 9862f89c3..4967671ca 100644
--- a/tests/test.h264.js
+++ b/tests/test.h264.js
@@ -51,7 +51,50 @@ async function haveH264Decode() {
 
     let support = await VideoDecoder.isConfigSupported(config);
     console.log(support);
-    _haveH264Decode = support.supported;
+    if (!support.supported) {
+        _haveH264Decode = false;
+        return false;
+    }
+
+    // Firefox incorrectly reports supports for H.264 under some
+    // circumstances, so we need to actually test a real frame
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=1932392
+
+    const data = new Uint8Array(Base64.decode(
+        'AAAAAWdCwBTZnpuAgICgAAADACAAAAZB4oVNAAAAAWjJYyyAAAABBgX//4Hc' +
+        'Rem95tlIt5Ys2CDZI+7veDI2NCAtIGNvcmUgMTY0IHIzMTA4IDMxZTE5Zjkg' +
+        'LSBILjI2NC9NUEVHLTQgQVZDIGNvZGVjIC0gQ29weWxlZnQgMjAwMy0yMDIz' +
+        'IC0gaHR0cDovL3d3dy52aWRlb2xhbi5vcmcveDI2NC5odG1sIC0gb3B0aW9u' +
+        'czogY2FiYWM9MCByZWY9NSBkZWJsb2NrPTE6MDowIGFuYWx5c2U9MHgxOjB4' +
+        'MTExIG1lPWhleCBzdWJtZT04IHBzeT0xIHBzeV9yZD0xLjAwOjAuMDAgbWl4' +
+        'ZWRfcmVmPTEgbWVfcmFuZ2U9MTYgY2hyb21hX21lPTEgdHJlbGxpcz0yIDh4' +
+        'OGRjdD0wIGNxbT0wIGRlYWR6b25lPTIxLDExIGZhc3RfcHNraXA9MSBjaHJv' +
+        'bWFfcXBfb2Zmc2V0PS0yIHRocmVhZHM9MSBsb29rYWhlYWRfdGhyZWFkcz0x' +
+        'IHNsaWNlZF90aHJlYWRzPTAgbnI9MCBkZWNpbWF0ZT0xIGludGVybGFjZWQ9' +
+        'MCBibHVyYXlfY29tcGF0PTAgY29uc3RyYWluZWRfaW50cmE9MCBiZnJhbWVz' +
+        'PTAgd2VpZ2h0cD0wIGtleWludD1pbmZpbml0ZSBrZXlpbnRfbWluPTI1IHNj' +
+        'ZW5lY3V0PTQwIGludHJhX3JlZnJlc2g9MCByY19sb29rYWhlYWQ9NTAgcmM9' +
+        'YWJyIG1idHJlZT0xIGJpdHJhdGU9NDAwIHJhdGV0b2w9MS4wIHFjb21wPTAu' +
+        'NjAgcXBtaW49MCBxcG1heD02OSBxcHN0ZXA9NCBpcF9yYXRpbz0xLjQwIGFx' +
+        'PTE6MS4wMACAAAABZYiEBrxmKAAPVccAAS044AA5DRJMnkycJk4TPw=='));
+
+    let error = null;
+
+    let decoder = new VideoDecoder({
+        output: frame => {},
+        error: e => { error = e; },
+    });
+    let chunk = new EncodedVideoChunk({
+        timestamp: 0,
+        type: 'key',
+        data: data,
+    });
+
+    decoder.configure(config);
+    decoder.decode(chunk);
+    await decoder.flush();
+
+    _haveH264Decode = error === null;
 
     return _haveH264Decode;
 }