The legacy extension must reside somewhere within your Firefox Profile. Look for *.rdf files inside your %user% folder (every add-on has one and one only RDF file).. Find the most probable candidate and check (btw rdf is an XML file) the entry em:maxVersion. Could be it is set to less than 22.

Surely it would prevent the XBAP displaying, not freezing the entire browser?

Hi, I have a similar problem. I did attempt the *.rdf fix on a test system, but it didn't work (em:maxVersion was already 22).

We got about inflow of phone calls from our clients experiencing the problem mentioned above from the 2nd of July onwards... and more are phoning in.

All the complaints come from clients (+- 10 so far and rising in number) using Firefox v22 (we have checked), and all of them have said that it was working previously.

We downgraded one of the clients to an older version of Firefox, and it worked again. So far we are telling our clients to downgrade until a fix comes out, or use Internet Explorer (*blush*)

Hi,We too have the same problem.But as our application is used by many of the customers, client is not accepting the downgraded the version to older version.Can we have any alternate work around.

When can we expect the permanent fix from the firefox team ,which supports Xbap in firefox.

Windows 7 doesn't include the WPF plug-in for Firefox.
http://msdn.microsoft.com/en-us/library/cc716877.aspx

Bug report was filed here.
https://bugzilla.mozilla.org/show_bug.cgi?id=893671
UNCONFIRMED [NEEDINFO]

See if this helps you - https://support.mozilla.org/en-US/kb/windows-media-or-other-plugins-stopped-working