diff --git a/browser/themes/gnomestripe/browser/engineManager.css b/browser/themes/gnomestripe/browser/engineManager.css
index 429fa8ca39ed..260d115741c1 100644
--- a/browser/themes/gnomestripe/browser/engineManager.css
+++ b/browser/themes/gnomestripe/browser/engineManager.css
@@ -40,6 +40,8 @@
 #engineList treechildren::-moz-tree-image(engineName) {
   -moz-margin-end: 4px;
   -moz-margin-start: 1px;
+  width: 16px;
+  height: 16px;
 }
 
 #engineList treechildren::-moz-tree-row {
diff --git a/browser/themes/pinstripe/browser/engineManager.css b/browser/themes/pinstripe/browser/engineManager.css
index 429fa8ca39ed..260d115741c1 100644
--- a/browser/themes/pinstripe/browser/engineManager.css
+++ b/browser/themes/pinstripe/browser/engineManager.css
@@ -40,6 +40,8 @@
 #engineList treechildren::-moz-tree-image(engineName) {
   -moz-margin-end: 4px;
   -moz-margin-start: 1px;
+  width: 16px;
+  height: 16px;
 }
 
 #engineList treechildren::-moz-tree-row {
diff --git a/browser/themes/winstripe/browser/engineManager.css b/browser/themes/winstripe/browser/engineManager.css
index 429fa8ca39ed..260d115741c1 100644
--- a/browser/themes/winstripe/browser/engineManager.css
+++ b/browser/themes/winstripe/browser/engineManager.css
@@ -40,6 +40,8 @@
 #engineList treechildren::-moz-tree-image(engineName) {
   -moz-margin-end: 4px;
   -moz-margin-start: 1px;
+  width: 16px;
+  height: 16px;
 }
 
 #engineList treechildren::-moz-tree-row {