It's funny. Over 20 years ago, I got people to switch to Firefox because of the AdBlock extension.

In case people don't know, Firefox was the first major browser to even have extensions.

There is only XUL!

Long dead. Now there is no XUL, only (private user) data (that Mozilla sells for revenue)

I think they're making a Ghostbusters joke, btw

Mozilla made the joke themselves, about Firefox. "There is no data, there is only XUL" was an official XUL catchphrase. But now there is no XUL, and Mozilla sells private user data, so it's reversed.

Also, Firebug showed what was possible with developer tools. Inspecting elements or network requests or whatever else wasn't really a thing before that extension.