When I activate WebARX, the theme editor option disappears. How can I turn it back on?

In order to make this option appear again while having the WebARX plugin activated, do the following:

1. Go to the admin panel of your site.
2. Go to Settings > Security
3. On the "Hardening" section, uncheck the "Disable plugin/theme edit" option.
4. Scroll down to the bottom of the page and click on "Save settings".