When a ToolBook generated DHTML lesson loads in Firefox, the browser immediately reports that:
Additional Plugins are required to display all the media on this page
and offers a button to "Install Missing Plugin", which will attempt to install the Windows Media Player plugin. However the Windows Media Player is already installed and even reinstalling it does not help.
The problem seems to have started occurring with the release of Firefox version 21.
The problem is not related to ToolBook at all, and instead is a general failure of Firefox to load browser plugins. Details about this, and a solution can be found here, on the Mozilla web site:
As extra verification that it is really a failure of the Windows Media Player to load within Firefox, you can try visiting this non-ToolBook web site, using Firefox:
which will attempt to load the Windows Media Player plugin, and play a video file. A failure of it to play means the plugin is not loading.
Created with the Personal Edition of HelpNDoc: Free EBook and documentation generator