CSS linking XBL just removes methods of the tag

Question

I want to extend the XUL browser tag with some methods but whenever I make the link in CSS it just removes methods from the tag. I can't tell if this is because the URI is wrong, or if the XBL file is wrong. Even the simplest XBL does this so it must be the URI. I was hoping to put my bindings in a "bindings" directory in chrome/content.

I have some JS which calls the loadURI method of the browser tag in question which is already working but the minute I link the binding to it it errors out telling me there is no such method. Remove the CSS binding and it works again.

#bwindow{
  -moz-binding:     url("chrome://nameofmyapp/content/bindings/browser.xbl#sbrowser");
}

The XBL I did originally is much more complex but when it didn't work I just went with a simple one.

<?xml version="1.0"?>
<bindings xmlns="http://www.mozilla.org/xbl"
        xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
         <binding id="sbrowser" extends="xul:browser">
            <content><xul:label value="blah" /></content>
         </binding>
</bindings>

The following is my chrome manifest. These seem to work. The skin definitely does.

content nameofmyapp content/
skin nameofmyapp default/1.0 skin/default/

The browser tag looks like this

<browser onload="browserload()" id="bwindow" type="content" src="about:blank" flex="1"/>

Again everything works fine until I link in the XBL with CSS to #bwindow