Mark top-level await supported behind a flag in Firefox 85 (#7584)

Author: saschanaz

javascript/operators/await.json

@@ -80,11 +80,22 @@
                 "version_added": false
               },
               "firefox": {
-                "version_added": false,
-                "notes": "See <a href='https://bugzil.la/1519100'>bug 1519100</a>"
+                "version_added": "85",
+                "flags": [
+                  {
+                    "type": "preference",
+                    "name": "javascript.options.experimental.top_level_await"
+                  }
+                ]
               },
               "firefox_android": {
-                "version_added": false
+                "version_added": "85",
+                "flags": [
+                  {
+                    "type": "preference",
+                    "name": "javascript.options.experimental.top_level_await"
+                  }
+                ]
               },
               "ie": {
                 "version_added": false