Simplify the following text for a Grade 7 native English-speaking person.
Original: Microsoft spent over US$ 100 million per year on Internet Explorer in the late 1990s , with over 1000 people working on it by 1999 .
Simplified: Microsoft spent over $ 100 million per year on IE in the late 1990s , with over 1000 people working on it by 1999 .