Unlike say OSX or Windows or Linux Android doesn't like having 2 browsers installed. Why would you want 2 browsers installed?
Well, maybe you prefer one but it's missing features. For example Opera supports websockets, the built in browser does not. Firefox supports WebGL the built in browser does not.
Maybe you want to keep one browser logged in to a certain account on a certain service and another browser logged in on a different account on the same service. Why would you want to do this? Because re-logging in on any phone sucks. Typing in names and passwords, especially "strong" passwords with upper/lowercase, numbers and symbols is no fun.
But, Android doesn't like 2 browsers installed. It asks "which browser" every time a link is clicked, every time the browser is redirected, and every time a browser is launched. If I set a default for clicking a link to browser 1 then clicking a link in browser 2 launches browser 1. WTF!? I know technically why it does this but it was arguably the wrong design.
