My students may be wondering why the video file supplied with their assignment plays properly in IE with an embed tag, but may not work in Firefox. It is because the author of your text book used a wmv media file which is a windows media format. The author is a PC centric developer. PCs running Windows can play it if the Windows media player is loaded on the machine and IE is the browser being used to view it. My guess is that the author had that set up and therefore did not run into problems as he was writing the book. Note: I have successfully played wmv file he supplied, using the embed tag as he suggested, with Safari on the Mac without incident. However, Firefox will not play it using the embed tag.
The following forum discussion on the Mozilla web site discusses this matter in length. Caution… it is technical. http://forums.mozillazine.org/viewtopic.php?t=206213
Many designers today prefer to use Flash to embed video. The Flash player is loaded on 99% of browsers on the internet. As such, media that has been converted to a .flv format to play through the Flash player will play with no problem through the majority of browsers. That is why Youtube, Blip, and most other video upload services use Flash as their media player. While that will not solve all of your design problems involving playing media files, it will meet the needs of the majority of your audience.
I am in the process of updating this course and will discontinue using the current book in the future. For now though, understand that many of the authors practices, while not standards or W3C compliant, are still coding practices you will encounter in the field. Knowing a bit about them will enhance your skills as a designer – especially if you are called to update an existing client web site.