In early versions of Netscape, any URI beginning with about: that wasn't recognized as a built-in command would simply result in the text after the colon being displayed.
Similarly, in early versions of Internet Explorer, about: followed by a string of HTML (e.g. about:hello world) would render that string as though it were the source of the page — thus providing a similar (though more limited) facility to the data: URI scheme defined by RFC 2397.
Still other versions of Netscape would return various phrases in response to an unknown about URI, including "Whatchew talkin' 'bout, Willis?"
(a catch phrase from the TV show Diff'rent Strokes) or "Homey don't play dat!"
[5] The following applies to all web browsers that derive from the Chromium project, including Google Chrome, Microsoft Edge, Opera, and Vivaldi.
On first use, about:config displays a message which tells the user that the settings might void the warranty and they can be "Harmful to the stability, security, and performance of this application."
Any about URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled."
It is a quote from Chapter 3 of Saint-Exupéry's memoir Terre des Hommes (titled Wind, Sand and Stars in its English translation by Lewis Galantiere).
Only developers who knew which file in the source tree and the encoding scheme used to obfuscate the directory of employee about entries could add their names.