Running Knoppix 6.7.1 on HD install. Upgraded Iceweasel to 10.0.2-1 with Synaptic, this also pulled in libmozjs10d (10.0.2-1), libvpx1 (1.0.0-2) and xulrunner-10.0 (10.0.2-1). xulrunner 9.0.1-1 and 1.9.1.16-11 remain installed from the original Knoppix HD install. Iceweasel now fails to start, returning an XML error:

XML Parsing Error: undefined entity
Location: chrome://browser/content/browser.xul
Line Number 553, Column 7:

<menuitem id="context-video-showstats"
------^

(NB: The caret on the last line appears under the "<" of the previous line ... the auto-removal of 'redundant' spaces in the forum post mechanism is changing the layout.)

This error also appears if you try to run 'Tools/Validate HTML' in Kompozer.

Help?