Well, most of us subscribe to the school who understand why it's wiser to use something open that has been checked-over by thousands of people.
Thankfully, the reasons this is wiser aren't rocket science for most people.

As Mozilla have nothing to hide, here's the source code for Firefox:
Click Here

As for Microsoft, here's the most you'll get for Internet Explorer:
Click Here

Take your time, Hornet, work it out.