diff --git a/dom/html/test/test_fullscreen-api-race.html b/dom/html/test/test_fullscreen-api-race.html
index 03c6c6da3aa5..3035711acc92 100644
--- a/dom/html/test/test_fullscreen-api-race.html
+++ b/dom/html/test/test_fullscreen-api-race.html
@@ -35,7 +35,9 @@ addLoadEvent(function () {
   SpecialPowers.pushPrefEnv({
     "set": [
       ["full-screen-api.unprefix.enabled", true],
-      ["full-screen-api.allow-trusted-requests-only", false]
+      ["full-screen-api.allow-trusted-requests-only", false],
+      // Use legacy data: URI behavior to run test.
+      ["security.data_uri.unique_opaque_origin", false]
     ]
   }, next);
 });