1404933 - WebExtensions can't create HTML UIs in XML documents

Status: RESOLVED DUPLICATE of bug 1401793

(WebExtensions :: Untriaged, defect)

Description

[mrmr1993]

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0
Build ID: 20170816210634

Steps to reproduce:

Open an XML document (e.g. https://search.maven.org/remotecontent?filepath=io/airbrake/logback/0.1.0/logback-0.1.0.pom)

Create a HTML element and insert it into the document, e.g. by running
  var el = document.createElementNS("http://www.w3.org/1999/xhtml", "div");
  document.documentElement.appendChild(el);


Actual results:

The displayed XML hierarchy collapses into a single line of text, with no styles.


Expected results:

The XML hierarchy is displayed unchanged, and the HTML element is added to the DOM and displayed in the page.


This bug[1] affects the Vimium-ff[2] extension, since we have to inject HTML into the active document to show our UI. Note that this works as expected in Chrome.

[1]: https://github.com/philc/vimium/issues/2690
[2]: https://addons.mozilla.org/en-US/firefox/addon/vimium-ff/