When you are on the site where the game is not loading, do you see a notification icon in the address bar?

The plugin notification icon typically looks like a small, dark gray Lego block. If you click it, it should tell you whether Flash is allowed for the page or whether you need to allow it.

If the icon doesn't appear, Firefox doesn't recognize the code in the page. If it does appear, and Flash is allowed, then the page may be having a hard time starting it up.

There is an issue with some Flash games not loading in Firefox 40. To see whether the game you are playing is affected by that issue (asynchronous loading), you could try this settings change:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste ipc and pause while the list is filtered

(3) Double-click the dom.ipc.plugins.asyncInit preference to switch its value from true to false

I don't know whether that starts taking effect immediately, or whether you need to exit Firefox and start it up again.

Then return to the page with the game and reload the page (you can click the circular arrow in the address bar) to see whether it will work now.

Any luck?

Hmm, I just looked at Question Details > More System Details for your post and it doesn't show the Flash plugin being activated. Either it is a very old version that has been disabled, or it has gone missing for some reason.

Could you download the full Flash plugin installer from this page:

https://www.adobe.com/products/flashplayer/distribution3.html

In the first table, look for the row for "plugin-based browsers" and you can use either the EXE or the MSI installer.

After downloading, go ahead and run it. You can trigger that from Firefox's download list (blue arrow on the toolbar).

Once that completes, check Firefox's Add-ons page to see whether Firefox discovered it. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. On the right, look for "Shockwave Flash". Is it there? Note that if it was previously disabled, it would be in a grayed section at the bottom and needs to be set to either "Always Activate" or "Ask to Activate".

In some cases, you might need to exit out of Firefox and start it up again to discover a newly installed plugin.

Any luck?