Yes you download it - close all other pgms and install it-

during the install it will ask a few questions - like -
- do you want it to be the default browser? { you can always change it later if you want to in the settings/options}
do you want to import favs/bookmarks etc ?

It will import your stuff - to be sure I usually save a copy/ back up in my documents or somewhere - i have even emailed them to my self a few times

hmm i should do that again it's been awhile..

I use FF most of the time but once in awhile I need to use IE for some sites - so IE still there It just depends on which one you open up.
If you set one or the other as the default then when you click a link or need to open one from a email or something then the default is the one opened.