Bug 1573485 - put developer tools button back on the right/end of the toolbar in devedition, r=pbro,jaws

Differential Revision: https://phabricator.services.mozilla.com/D43599

--HG--
extra : moz-landing-system : lando

browser/components/customizableui/CustomizableUI.jsm

@@ -233,7 +233,7 @@ var CustomizableUIInternal = {
     ];
 
     if (AppConstants.MOZ_DEV_EDITION) {
-      navbarPlacements.splice(2, 0, "developer-button");
+      navbarPlacements.splice(7, 0, "developer-button");
     }
 
     this.registerArea(