Most videos and web games use Adobe Flash Player to play, in which case you would only require Adobe Flash Player. Many websites are also moving into HTML5, which should be natively supported within Firefox.

If you experiencing issues with buffering or slow response times in web games, it may be because your system is not up to the current standards. As technology progresses, many websites are requiring more computer resources, meaning that many older systems will notice a decrease in performance.

If you are having issues, it may be a good idea to investigate upgrading your system or purchasing a new system.

Locking this thread, please continue in your original thread about this subject matter. "One thread to a customer."

https://support.mozilla.org/en-US/questions/1131138