Firefox Problem

hi folks,

I have a weird situation here. I use jw player with progressive download (just 2 videos, did not bother using streaming), in the site below. When the user tries to seek forward, in Firefox, the audio continues to play, but the video goes dark. I also tried in IE8 and Chrome, and it behaves as expected: can not seek to non-downloaded part, but continues to play. I could not find any clues what might be causing this.

here is the video address: http://www.adaptivecurriculum.com/us/video-activity-object.html

You can find the code in the page source there. Any help will be appreciated.