diff --git a/.gitignore b/.gitignore
index 8e82cd43d5a0..6c9ba74f8ab2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -191,6 +191,9 @@ lextab.py
 !.vscode/tasks.json
 *.user
 
+# Thunderbird source tree
+/comm/
+
 # Ignore various raptor performance framework files
 testing/raptor/.raptor-venv
 testing/raptor/raptor-venv