diff --git a/ext/fg/js/document.js b/ext/fg/js/document.js
index 9afc44f0..94a68e6c 100644
--- a/ext/fg/js/document.js
+++ b/ext/fg/js/document.js
@@ -267,6 +267,9 @@ const caretRangeFromPoint = (() => {
         // Firefox
         return (x, y) => {
             const position = document.caretPositionFromPoint(x, y);
+            if (position === null) {
+                return null;
+            }
             const node = position.offsetNode;
             if (node === null) {
                 return null;