windows media plugin fails to play video, audio OK. Plugin in FFox 18.0.2 under W7. Fails win media test.

Symptom: MS Office 7 "Help" video selection triggers Ffox 18.0.2 browser which attempts to open aspx video and plays the soundtrack but does not display the visual content. Diagnosis: WM player plugin enabled and up to date. Ffox support page for WM Player plugin Windows Media Test link causes message/prompt "Not found: litmus-data/raw-file/tip/firefox/plugins/mediaplayer.html" on a Mercurial page. FAQs do not detail the problem or solution. Any ideas? Just tried pasting the aspx link into Chrome address bar and the video plays correctly. I presume this means that WMP and codecs are installed correctly and the FFox (MZ) plugin is not linking properly with MZ.