So it served it's purpose - you downloaded Firefox - and never used it again.The problem with IE is it was impossible to remove. It was so integrated in that you were required to have it on your computer zero other choice. Mix that with forced default and trying to hide the fact there were alternatives.
I remember back then IE for me served one purpose and it was to download Firefox.
You could default to another browser. Problem solved.
Just because it stayed on your computer and was tied to the OS doesnt mean Microsoft weren't somehow using it or parts of it (APIs) to do other tasks. How many lines of legacy code exist in Windows? Lots just sit there because everyone is too scared to remove it. Just. In. Case.