diff --git a/srcpkgs/firefox-esr/files/mozconfig b/srcpkgs/firefox-esr/files/mozconfig
index 31bb6dcd0f2..708ee9eded9 100644
--- a/srcpkgs/firefox-esr/files/mozconfig
+++ b/srcpkgs/firefox-esr/files/mozconfig
@@ -32,3 +32,4 @@ ac_add_options --enable-optimize="$CFLAGS"
 
 ac_add_options --enable-official-branding
 ac_add_options --enable-application=browser
+ac_add_options --allow-addon-sideload