diff --git a/pkgs/applications/networking/mailreaders/thunderbird/91/D124361.diff b/pkgs/applications/networking/mailreaders/thunderbird/91/D124361.diff
new file mode 100644
index 00000000000..42dee06a26b
--- /dev/null
+++ b/pkgs/applications/networking/mailreaders/thunderbird/91/D124361.diff
@@ -0,0 +1,22 @@
+diff --git a/comm/mail/config/mozconfigs/common b/comm/mail/config/mozconfigs/common
+--- a/comm/mail/config/mozconfigs/common
++++ b/comm/mail/config/mozconfigs/common
+@@ -1,6 +1,3 @@
+ ac_add_options --enable-application=comm/mail
+ 
+-# Disable enforcing that add-ons are signed by the trusted root.
+-MOZ_REQUIRE_SIGNING=
+-
+ . "$topsrcdir/build/mozconfig.common.override"
+diff --git a/comm/mail/moz.configure b/comm/mail/moz.configure
+--- a/comm/mail/moz.configure
++++ b/comm/mail/moz.configure
+@@ -12,6 +12,7 @@
+ imply_option("MOZ_CRASHREPORTER_URL", "https://crash-reports.thunderbird.net/")
+ 
+ imply_option("--enable-default-browser-agent", False)
++imply_option("MOZ_REQUIRE_SIGNING", False)
+ 
+ 
+ @depends(target_is_windows, target_is_linux)
+
diff --git a/pkgs/applications/networking/mailreaders/thunderbird/91/default.nix b/pkgs/applications/networking/mailreaders/thunderbird/91/default.nix
index f00f85336b6..5f86af60b4f 100644
--- a/pkgs/applications/networking/mailreaders/thunderbird/91/default.nix
+++ b/pkgs/applications/networking/mailreaders/thunderbird/91/default.nix
@@ -11,6 +11,12 @@ callPackage (import ../../../browsers/firefox/common.nix rec {
   };
   patches = [
     ./no-buildconfig-90.patch
+
+    # There is a bug in Thunderbird 91 where add-ons are required
+    # to be signed when the build is run with default settings.
+    # https://bugzilla.mozilla.org/show_bug.cgi?id=1727113
+    # https://phabricator.services.mozilla.com/D124361
+    ./D124361.diff
   ];
 
   meta = with lib; {