diff --git a/toolkit/themes/gnomestripe/global/alerts/alert.css b/toolkit/themes/gnomestripe/global/alerts/alert.css
index 69b6412b58cb..072923dbd295 100644
--- a/toolkit/themes/gnomestripe/global/alerts/alert.css
+++ b/toolkit/themes/gnomestripe/global/alerts/alert.css
@@ -27,6 +27,11 @@
   min-width: 46px;
 }
 
+#alertImage {
+  max-width: 48px;
+  max-height: 48px;
+}
+
 .alertTitle {
   font-weight: bold;
 }
diff --git a/toolkit/themes/winstripe/global/alerts/alert.css b/toolkit/themes/winstripe/global/alerts/alert.css
index 688a6f0c1f4a..1d70096e0c29 100644
--- a/toolkit/themes/winstripe/global/alerts/alert.css
+++ b/toolkit/themes/winstripe/global/alerts/alert.css
@@ -32,6 +32,11 @@
   font-weight: bold;
 }
 
+#alertImage {
+  max-width: 48px;
+  max-height: 48px;
+}
+
 .alertText {
   -moz-margin-end: 6px;
 }