You think more than 50% of the people using Firefox or (especially) Internet Explorer deliberately sought it out and installed it after making an informed decision?
I'm not even talking about tricks. IE comes pre-installed on all PCs, obviously, except for Europeans, and that only for a few years. But users generally do not bother performing in-depth research on the software they install, be it a browser some other piece of software. They use what that one technical friend keeps blabbering on about, or what their sysadmin installs on their work PC, or whatever comes up as #1 Google result when they search for 'open PDF file'. They intentionally install Firefox, true, but I am not convinced that decision is informed.
