@amachini, be careful with this sort of thing 
Put this below 'sudo' command in your terminal, and Firefox will be gone.
sudo apt-get remove --purge firefox
In some OS's there could be other programs that depend on Firefox; and removing Firefox would remove these programs as well - I do not know about U-MATE.
If you don't like Firefox, then don't use it. You can remove it from your menus; but I would think twice about uninstalling it. A backup browser can be a good thing.
Well, Linux is freedom so there is the command to take out most programs (without that last firefox part, unless its firefox)