I don't think that many people make plans five years in advance, especially if what they are using happens to work well for them. I was happy using an IE clone, Avant Browser and then Maxthon until Firefox came on the scene.
I watched it progress and tried one of the early builds and it was a bit too early for me, I the 1.5 version where I used it as my default browser and I haven't looked back. It is a highly configurable browser with great add-on support which allows for greater security and user functionality.
I have in the interim tried Opera and Chrome a couple of times. I couldn't live with the Opera interface (I had tried this many times before I used firefox also). Chrome, great name but needed a good deal more finishing (buffed up), the page loading speed increases (marginal in my case) couldn't make up for its lack of configuration and add-on support.
So I'm not looking 5 years down the line, but monitor what is happening now, 6 months and possibly 12 months. Crucially I generally don't go looking if what I have works for me. If that time comes when firefox doesn't meet my needs, I'm not tied to it for life.