diff --git a/sway/behaviours b/sway/behaviours
index fe45cd96e..0bf16d215 100644
--- a/sway/behaviours
+++ b/sway/behaviours
@@ -8,6 +8,7 @@ assign [class="Mattermost"] 1
 assign [class="Rocket.Chat"] 1
 assign [class="UXTerm"] grave
 assign [class="Thunderbird"] 2
+assign [class="thunderbird-default"] 2
 assign [app_id="thunderbird"] 2
 assign [class="Chromium"] 3
 assign [class="Linphone"] 5