--- a/browser/components/customizableui/PanelMultiView.jsm
+++ b/browser/components/customizableui/PanelMultiView.jsm
@@ -823,16 +823,22 @@ this.PanelMultiView = class {
         // Now that the main view is visible, we can check the height of the
         // description elements it contains.
         this.descriptionHeightWorkaround();
         break;
       case "popuphidden":
         this.node.removeAttribute("panelopen");
         this.showMainView();
         if (this.panelViews) {
+          for (let panelView of this._viewStack.children) {
+            if (panelView.nodeName != "children") {
+              panelView.style.removeProperty("min-width");
+              panelView.style.removeProperty("max-width");
+            }
+          }
           this.window.removeEventListener("keydown", this);
           this._panel.removeEventListener("mousemove", this);
           this._resetKeyNavigation();
           this._mainViewHeight = 0;
         }
         break;
     }
   }

--- a/browser/themes/shared/customizableui/panelUI.inc.css
+++ b/browser/themes/shared/customizableui/panelUI.inc.css
@@ -341,16 +341,19 @@ panelview:not([mainview]) .toolbarbutton
 #appMenu-popup > .panel-arrowcontainer > .panel-arrowcontent {
   padding: 0;
   border-radius: 0;
 }
 
 photonpanelmultiview panelview {
   background: var(--arrowpanel-background);
   padding: 6px 0;
+}
+
+#appMenu-popup panelview {
   min-width: @menuPanelWidth@;
 }
 
 photonpanelmultiview panelview[title] {
   padding-top: 0;
 }
 
 photonpanelmultiview .panel-subview-body {