- Upgrade your Magento 2 installation at least to the 2.1.0-rc1.
- Learn the article How is the main frontend menu generated? (from Magento 2.1.0-rc1).
- Create a
before-
plugin to the\Magento\Theme\Block\Html\Topmenu::getHtml()
method, similar to the core’s one from the Step 2, and set a negative value for it’ssortOrder
.