This is a follow up from my comments on PR #4191

Currently these are the URL schemes that we support in the URL plugin.

private static readonly string[] UrlSchemes = ["http://", "https://", "ftp://"];

As far as I can tell browsers no longer support the ftp protocol for security reasons

https://developer.chrome.com/blog/chrome-88-deps-rems#ftp_support_removed
https://blog.mozilla.org/security/2021/07/20/stopping-ftp-support-in-firefox-90/

Given that - it would be best to remove support on our end too, since it won't work for users anymore.

But beyond that it might be worth supporting more scheme types that work for browsers

Of note is internal addresses like chrome:// which is requested in issue #4014
The equivalent for firefox is about: I believe
chrome-extension:// is another of that kind

Apart from those internal addresses we also have ones like view-source: and file://