Bug 1414244 - Part 1 - Remove the "panelid" attribute. r=Gijs

MozReview-Commit-ID: 4o27h6PhCRg

--HG--
extra : rebase_source : 7be0dd97832033fa0d5304afd0def1cd3dcd3ddf

browser/components/customizableui/PanelMultiView.jsm

@@ -306,8 +306,6 @@ this.PanelMultiView = class {
     } else {
       this._clickCapturer.addEventListener("click", this);
 
-      this._mainViewContainer.setAttribute("panelid", this._panel.id);
-
       if (this._mainView) {
         this.setMainView(this._mainView);
       }

browser/themes/shared/customizableui/panelUI.inc.css

@@ -1300,7 +1300,6 @@ menuitem[checked="true"].subviewbutton > .menu-iconic-left {
   visibility: hidden;
 }
 
-.panel-mainview[panelid=customizationui-widget-panel],
 #PanelUI-panicView > .panel-subview-body,
 #PanelUI-panicView {
   overflow: visible;