Can you post a link to a publicly accessible page (i.e. no authentication or signing on required)?

Note that this can happen if the website tries to embed an HTML file via an <embed> tag and this won't work in Firefox.

You can check that via the right-click context menu in the Inspector. You can right-click and select "Inspect Element" to open the Inspector ("3-bar" menu button or Tools > Web Developer) with this element selected.

• https://developer.mozilla.org/Tools/Page_Inspector
• https://developer.mozilla.org/Tools/Page_Inspector/How_to

http://www.mnfclub.com/game.html

That is about the Shockwave Flash plugin plugin.

Your system details list doesn't show the Shockwave Flash plugin as installed and enabled.

• Firefox/Tools > Add-ons > Plugins

You can find links of the latest Shockwave Flash player for Firefox on this page:

• http://www.adobe.com/special/products/flashplayer/fp_distribution3.html

You can verify on the Adobe Flash Players Test Page that the Flash plugin is working and which version you have.

• http://www.adobe.com/software/flash/about/