How could a strange toolbar suddenly pop out in my window?

When I open my Mozilla window suddenly there’s a new toolbar called “Kiwee” that stick in my window each time I open my Mozilla window. This is not the first time,last month the same toolbar called “SweetIM” also stick in my window but I ignored it since I thought it will do no harm,but now there are too many toolbars and that really mess up my window and it also automatically change my browser each time I open a new tab.

So I want to know where these toolbars came from?,since I don’t even install/download these things.
How could I fix/block these toolbars so I won’t have to deal with the same issue again?