See upcoming testcase. I've a xbl-ized textarea and in the xbl binding I've added some content. In the dom tree I can see this content is successfully added, but it's not becoming visible. A regular dom method is working, so I would think that the xbl should also work, not?

The textarea shows its kids. Period. XBL doesn't add any kids to the textarea (it just adds anonymous content which the textarea doesn't know about). We could hack this to work, possibly, but that would basically need major changes to Editor and I don't think it would be the right thing in any case.

I think this might have become invalid. The patch for bug 152329 has specifically shut down the rendering of textinput elements. So the dynamically appended div is also not rendering anymore.