diff --git a/appdefs.xml b/appdefs.xml
index 4c78da6..ce36ec0 100644
--- a/appdefs.xml
+++ b/appdefs.xml
@@ -107,6 +107,11 @@ details.
     </documentation>
     <!-- Changelog of the application. -->
     <history>
+      <release>
+        <version>1.5.1</version>
+        <date>2019-05-12</date>
+        <change>Upgraded Firefox to version 66.0.5-r1.</change>
+      </release>
       <release>
         <version>1.5.0</version>
         <date>2019-05-09</date>