Unless you visit about:about page in Firefox browser, you don’t know Firefox has this many internal pages, they are there for different purposes, of them, mostly, you use, about:config, about:support, about:profiles and about:performance to change a preference or to troubleshoot issues or to create a new profile or to see which tabs/pages are consuming more resources.
For some, you use options provided in the menu or Firefox UI. For instance, you can visit add-ons manager by visiting about:addons, but most prefer to click on the menu and choose add-ons, same the case with about:preferences as people select options in hamburger menu. Mozilla wants to ensure address bar should autofill the about: page you want to visit when you type about: and the first letter and list all URIs in drop-down that starts with that letter.
For instance, when you type about:c, about:cache will be auto-completed and all Firefox about: URIs that contain about:c will be populated and shown below for selection. The feature is now working in Firefox 64 Nightly.
Which about page do you visit most in Firefox? About:config?