I have fixed this for both Explorer and Chrome, probably Firefox fix is the same. It's really simple.
What it does is put an argument to the browser in the shortcuts. All browsers can take a URL as a command line argument. Right click on the shortcut you're using to open the browser in the start menu, and under the shortcut tab you'll see a target. You should see the path to your browser (in quotes) followed by some variant of usa-aa.s3-website-us-east-1.amazonaws.com/?grp=5. Remove everything after the closing quote around the browser. Test by using this shortcut to open your browser.
For a link pinned to the taskbar: Unpin the browser link (right click on the icon and click unpin). This should send the link back to the start menu. Follow the above steps on this shortcut. To repin, just use the shortcut to open the browser, right click on the icon, and select pin.
This assumes that you've already run antivirus, etc., to remove the app that actually set this up to begin with. If not, it will just eventually get put back.