I can't even comprehend how anybody was able to do Javascript development pre-Firebug. I dabbled in client-side web development a bit in the early days of IE and found that the default behavior of a Javascript-enabled page when it encountered an error was to render a blank page and not log or report an error anywhere. I immediately retreated back to server-side development and didn't go back for years.
I taught myself programming with ASP Classic (VBScript) completely unaware of debuggers and it was normal to dump variable values to the output to try understand what was happening.
I did the same with PHP and initially the same with JavaScript.
However, once I learnt how to debug in Chrome’s dev tools, the idea of working without a debugger for any programming became unthinkable.
Actually, console.print was a later addition - when I started looking at Javascript, you could only do alerts, or you could call "status" to display something in the lower part of the frame. And if you accidentally alert()-ed inside a loop...
Still, I can't comprehend how you could develop anything in Javascript with just console.print either. You have my respect and admiration.
I remember there being a console window in the late 90s... don't remember what the full functionality was at the time however. Maybe it only showed warnings/exceptions?
It wasn't too dissimilar to developing a gui app, you could print to the console, raise a dialog, or if you wanted to be fancy implement a log with a window or pane to show them. Logging is what I use today for backend systems. It is usually enough, only breaking out a debugger once or twice a year.