--- a/browser/base/content/browser.css
+++ b/browser/base/content/browser.css
@@ -729,17 +729,18 @@ html|input.urlbar-input[textoverflow]:no
 #main-window[customizing] :-moz-any(#urlbar, .searchbar-textbox) > .autocomplete-textbox-container > .textbox-input-box {
   visibility: hidden;
 }
 
 /* Flexible spacer sizing (matching url bar) */
 toolbarpaletteitem[place=toolbar][id^=wrapper-customizableui-special-spring],
 toolbarspring {
   -moz-box-flex: 1;
-  min-width: 0;
+  min-width: 28px;
+  max-width: 112px;
 }
 
 #nav-bar toolbarpaletteitem[id^=wrapper-customizableui-special-spring],
 #nav-bar toolbarspring {
   -moz-box-flex: 80;
 }
 
 /* ::::: Unified Back-/Forward Button ::::: */