--- a/toolkit/mozapps/extensions/content/extensions.css
+++ b/toolkit/mozapps/extensions/content/extensions.css
@@ -170,8 +170,12 @@ xhtml|link {
 #discover-view:not([selectedIndex="0"]) .loading {
   display: none;
 }
 
 /* Elements in unselected richlistitems cannot be focused */
 richlistitem:not([selected]) * {
   -moz-user-focus: ignore;
 }
+
+#header-search {
+  width: 22em;
+}

--- a/toolkit/mozapps/extensions/content/extensions.xul
+++ b/toolkit/mozapps/extensions/content/extensions.xul
@@ -195,17 +195,17 @@
                   accesskey="&updates.resetUpdatesToAutomatic.accesskey;"
                   command="cmd_resetAddonAutoUpdate"/>
         <menuitem id="utils-resetAddonUpdatesToManual"
                   label="&updates.resetUpdatesToManual.label;"
                   accesskey="&updates.resetUpdatesToManual.accesskey;"
                   command="cmd_resetAddonAutoUpdate"/>
       </menupopup>
     </toolbarbutton>
-    <textbox id="header-search" type="search" searchbutton="true" size="35"
+    <textbox id="header-search" type="search" searchbutton="true"
              placeholder="&search.placeholder;"/>
   </hbox>
 
   <hbox flex="1">
 
     <!-- category list -->
     <richlistbox id="categories" persist="last-selected">
       <richlistitem id="category-search" value="addons://search/"