A Custom Domain, sometimes called a vanity URL, is a way to create links that include your brand.
When a link includes yourbrand, it helps people recognize and associate your links with your product or company. When they see your brand, they trust your links, and that results in higher click-through rates.
Custom domains + FireLinks
To use a custom domain in FireLinks, it must be no more than 32 characters long, including the dot.
Purchasing or adding a Custom Domain in your FireLinks account replaces the FireLink's short links with your own custom domain.
For example, when ESPN shortens a link through FireLinks, instead of being branded with FireLinks's domain (firelinks.io/wG8qhgpn)t he link displays their own custom domain (es.pn/2Qw1wd7).
By editing the end of the URL - we call that the back-half - you can further customize the link to be an even more identifiable Custom Branded Link, likees.pn/superbowl.