Add helper-script for the default browser to fix isues with firefox and root user

share/kali-themes/default-browser

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+if [ $(id -u) -eq 0 ]; then
+  USER=$(find $XAUTHORITY -printf '%u')
+  exec runuser -u $USER -- sensible-browser "$@"
+else
+  exec sensible-browser "$@"
+fi