No preview on the Firefox page. Please help.

When I want to see my my web page with flv video on preview window it is OK. I can watch the video. There is an orange colored button that enables the video to be played. However, if this page with flv video is intended to be played on the Firefox browser window this becomes impossible to be played. This time there is no orange colored play button. I tried to play the same flv video on the Explorer browser window there appeared an Active X related message, something like ''Do you want Explorer to enable Active X files?''. Firefox does not give such a message.
In fact I have never had such a problem before. I think I accidentally deleted or changed some Active X related files. I bring the video frame to the front layer.

I tried the same web page desing on different computers and got the same result. I am assuming that something goes wrong with my webpage design file.
Any help will be appreciated.

I have solved the problem. I moved the video player placeholder to the front layer and then the video became playable on the web browser preview.