Gecko sync update (#8959)

Co-authored-by: Suzy Liu <36471371+szy196@users.noreply.github.com>

Author: moz-wptsync-bot

css/css-flexbox/balance/META.yml

@@ -55,3 +55,9 @@ links:
     subtest: e.style['flex-wrap'] = "balance wrap-reverse" should set the property
       value
   - test: balance-negative-margin-001.html
+- product: firefox
+  url: https://bugzilla.mozilla.org/show_bug.cgi?id=2040109
+  results:
+  - test: balance-start-bias-001.html
+  - test: balance-start-bias-002.html
+  - test: balance-start-bias-003.html