Then again Firefox was itself a strip down of a rewritten Netscape suite. Stripped down in that the suite included not just a browser but also a email client, I

Then again Firefox was itself a strip down of a rewritten Netscape suite. Stripped down in that the suite included not just a browser but also a email client, IRC client and a HTML editor, and the UI was done using JS and XUL markup. What Firefox devs did was to take the browser part, make it stand alone, and replace much of the XUL UI with native widgets (GTK on _nix).