diff --git a/lib/main.js b/lib/main.js
index 304608c..b9c8a9b 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -87,7 +87,7 @@
 
             // Restore the maxlength value
             maxLength = elem.getAttribute(ATTR_MAXLENGTH);
-            if (maxLength) {
+            if (parseInt(maxLength, 10) >= 0) { // Old FF returns -1 if attribute not set (see GH-56)
                 elem.setAttribute("maxLength", maxLength);
                 elem.removeAttribute(ATTR_MAXLENGTH);
             }