If you wants to install flash for any browser just visit http://get.adobe.com/flashplayer/ from that browser and click on "Install Now" button to install flash player for that browser.
But since i have found that raptr is a standalone game so raptr support team would be the right contact who can guide you well that which Flash player plugin they are using in their game. And this is what i have found on there support page Raptr wants me to download "Flash for Other Browsers". Where do I get that? : Raptr Support
You can follow the steps on that link, I hope it will solve your problem.