diff --git a/home/wm/niri/config.kdl b/home/wm/niri/config.kdl
index 278350c..db6241a 100644
--- a/home/wm/niri/config.kdl
+++ b/home/wm/niri/config.kdl
@@ -70,6 +70,11 @@ layout {
     }
 }
 
+window-rule {
+  match app-id="firefox" title="Library"
+  default-column-width { proportion 0.40; }
+}
+
 window-rule {
   match app-id="virt-manager" title="Virtual Machine Manager"
   default-column-width { proportion 0.25; }