Apply workaround for Firefox bug (#6630)

* Apply workaround for Firefox bug
and shallow routing

* Update to only apply workaround when needed

* Add TODO for future removal
Co-Authored-By: Nijjk <22380829+ijjk@users.noreply.github.com>

packages/next-server/lib/router/router.js

-/* global __NEXT_DATA__ */
+/* global __NEXT_DATA__, location */
 
 import { parse } from 'url'
 import mitt from '../mitt'
@@ -40,6 +40,16 @@ export default class Router {
       this.changeState('replaceState', formatWithValidation({ pathname, query }), as)
 
       window.addEventListener('popstate', this.onPopState)
+
+      // Workaround for weird Firefox bug, see below links
+      // https://github.com/zeit/next.js/issues/3817
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=1422334
+      // TODO: let's remove this once the Firefox bug is resolved
+      if (navigator.userAgent && navigator.userAgent.match(/firefox/i)) {
+        window.addEventListener('unload', () => {
+          if (location.search) location.replace(location)
+        })
+      }
     }
   }