> Mozilla (including Firefox) had XUL, but nobody cared.

Have you seen XUL? Here's an example, from https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Tu...

    <?xml version="1.0"?>
    <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
    <window id="findfile-window"
            title="Find Files"
            orient="horizontal"
            xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
    
      <button id="find-button" label="Find"/>
      <button id="cancel-button" label="Cancel"/>
    
    </window>

All that does is display a window with two buttons. You can imagine how hideous it could get when it got more complex. Now, imagine this alternative (I'm assuming that id & title are mandatory arguments, and that orient is optional, default to horizontal):

    (sul
     (stylesheet "chrome://global/skin" "text/css")
     (window "findfile-window" "Find Files"
             (button "find-button" "Find")
             (button "cancel-button" "Cancel")))

Which would you rather write in?

Now, imagine that JavaScript were Scheme or Lisp instead, so that your browser interaction code were also written in an s-expression language. And imagine that CSS were s-expression-based, so that you were using the same tools to manipulate the same data everywhere.

It makes me weep.

Was it ever meant for general web usage?