That's a great attitude for saving money on cars and appliances, but it isn't always so great when it comes to technology.
A properly maintained car or appliance can easily last a decade or two, and it will keep working like it did the day you bought it.
Most tech gadgets, however, are considered old after just a few years. And even if they seem to be working correctly, there are likely serious problems lurking beneath the surface.
I'm sure you've heard that the main reason to upgrade your browser is new features. The latest browsers support HTML 5, they render Web pages faster, tabbed browsing is improved, and so on.
All of that is important and does make browsing the Internet much, much nicer. But if you're happy with your current browser, that's not much of an incentive to upgrade.