--- a/browser/themes/shared/customizableui/panelUI.inc.css
+++ b/browser/themes/shared/customizableui/panelUI.inc.css
@@ -348,16 +348,17 @@ panel[photon] > .panel-arrowcontainer > 
 photonpanelmultiview panelview {
   background: var(--arrowpanel-background);
   padding: 6px 0;
 }
 
 #appMenu-popup panelview,
 #customizationui-widget-multiview panelview:not([extension]) {
   min-width: @menuPanelWidth@;
+  max-width: 30em;
 }
 
 photonpanelmultiview panelview[title] {
   padding-top: 0;
 }
 
 /* END photonpanelview adjustments */