diff --git a/css/properties/appearance.json b/css/properties/appearance.json
index d7b6073dc090a4..39129699a76922 100644
--- a/css/properties/appearance.json
+++ b/css/properties/appearance.json
@@ -120,7 +120,14 @@
               "chrome_android": "mirror",
               "edge": "mirror",
               "firefox": {
-                "version_added": false
+                "version_added": "149",
+                "flags": [
+                  {
+                    "type": "preference",
+                    "name": "layout.css.appearance-base-select.enabled",
+                    "value_to_set": "true"
+                  }
+                ]
               },
               "firefox_android": "mirror",
               "oculus": "mirror",
@@ -187,7 +194,14 @@
                 "chrome_android": "mirror",
                 "edge": "mirror",
                 "firefox": {
-                  "version_added": false
+                  "version_added": "149",
+                  "flags": [
+                    {
+                      "type": "preference",
+                      "name": "layout.css.appearance-base-select.enabled",
+                      "value_to_set": "true"
+                    }
+                  ]
                 },
                 "firefox_android": "mirror",
                 "oculus": "mirror",