Firefox usually will require you to approve installing an add-on (particularly an extension), because they have access to everything you do in Firefox.

I don't think most games require their own add-ons. You might consider trying some other games that just run in the Flash player.

Buy a good anti-virus program. Most will scan all downloads automatically. Also, they will scan a program before it is allowed to run. You can get started with a free program from Microsoft.

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Use a compressed image type like PNG or JPG to save the screenshot.