If you're looking at a read only Webflow version of this site, you won't be able to see this through Webflow. Follow the instructions below.
If you're reading this from your browser, inspect this page and look at the custom scripts just before the closing </head> tag. You should see 3x <script>...</script>. These 3 scripts are placed here to be made available site wide.
Inspect this page and look at the custom scripts just before the closing </body> tag. You should see 2x <script>...</script>. These 2 scripts are placed here to be made available site wide, but it is not necessary for them to be in the head code.
You can see this by looking at the Custom Code section of each page in the Webflow designer.
This page contains the most code anywhere on this example site. The functionality can be boiled down to:
This page contains some simple head code which sets up the FirebaseUI authentication widget and displays it in the Log In / Sign Up page.