Problem is not related to Revolution slider or theme. Seems something is wrong with your previously uploaded images ( http://prntscr.com/kvsn1ohttp://prntscr.com/kvsnji )and FF does not load them. We have checked your old image and one new image that we uploaded when the default WP theme is activated. Your old image is not shown even with the default theme when we are trying to check it on the frontend https://gyazo.com/d4b938a299fdc6c3e15d672619c8936e
