I think I found the problem. Quicktime is having trouble with the 'mpeg' videos in the gallery. The solution I've found is to change firefox to use windows media player instead of quicktime.

In firefox, go to tools->options.

When the dialog opens click on the 'applications' icon.

In the list of 'content types' find the two labeled:

'Movie Clip (video/mpeg)'
'Movie Clip (video/x-mpeg)'

Change the associated viewer from the quicktime plugin to 'always ask' or 'other' then choose windows media player from the next dialog.

I'll try that, the message I get is:

Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file.

Thanks Bambam for your help.

Those two weren't really labelled. Not specifically like the way you suggest anyway.