Steps to reproduce:
0) Don't have sidebar extension enabled
1) Start ephy, enable sidebar extension
2) Go to bugzilla.mozilla.org
3) Click the "Add to sidebar" link

Expected results:
Adds to sidebar.

Actual result:
2 Errors in js console:

Error:
win has no properties

Javascript error in  on line 0:
uncaught exception: [Exception... "'[JavaScript Error: "win has no properties"
{file: "file:///opt/firefox/lib/firefox-1.0/components/nsSidebar.js" line: 93}]'
when calling method: [nsISidebar::addPanel]"  nsresult: "0x80570021
(NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)"  location: "JS frame ::
https://bugzilla.mozilla.org/ :: addSidebar :: line 49"  data: yes]

Seems like it uses mozilla's sidebar impl in this case (and fails since we're
embedded).