Adding on to what has already been mentioned.
Make sure your internet settings hasn't changed, there could be a possibility that there is something wrong with the browser you are using. As Shurtle mentioned, try switching browsers and keep the tab up and running during the entire time you're playing FH. Don't minimize it no matter what, even if it's after a minute.
Try seeing if you can restart the router as Enoki mentioned. If there was some sort of changes that has occurred, it could be the problem as well, like, if something changed in the internet setting of the provider.