With the "PC versus Mac" debate now approaching its fourth decade, the arguments from each side have necessarily become rather stale. How many times can we hear "Macs are too expensive," or "Windows always crashes," before it starts sounding like "Pepsi tastes better," or "Picard had more dignity"?

But in recent years, a new argument has emerged to rival the fervor of the operating-system zealots. It has more sides, more participants, and even more details to nitpick. It transcends age, class, familiarity with computers, and yes -- even operating systems.

Prepare for comment threads to stretch into the thousands when someone innocently asks, "Which web browser is the best?"

A decade ago, there was almost no question -- because there was almost no choice. Microsoft (MSFT) Internet Explorer had soundly beat Netscape through bigger budgets, advertising, proprietary codes, and pre-installations. Apple's (AAPL) Safari hadn't yet arrived, and Opera's browser was, well, about as popular as it is today. Internet Explorer was clearly the reigning champion.

Then in 2004, something unexpected occurred. As Microsoft rested on its laurels (and offered only slow and buggy updates to its browser), some former Netscape developers regrouped and released Mozilla Firefox -- a fantastic achievement in open-source software. With unique add-ons and a tremendous user base, Firefox expanded until it was a real competitor against the IE behemoth.

This week, the latest version of Firefox was released, boasting private browsing, a smaller memory footprint, faster load times, and countless other features. Though Microsoft has made notable improvements to the eight version of Internet Explorer, the software giant must face a diminishing market share: It's down to 65.5%, while Mozilla's plucky little project now commands 22.5%.

But wait -- if that only adds up to 88%, who's taking up the other 12%?

The answer: Many, many others.

Firefox's success flung open the doors to companies both big and small to develop their own method of surfing the web -- and actually acquire an audience willing to give their browser a test-run. Aside from Safari and Opera, there's Camino, Amaya, Konqueror, Flock, and most notably, Google's (GOOG) Chrome.

Safari is in its fourth incarnation, and Apple touts its load times as the fastest. Google continues to iron out the kinks in Chrome, but the browser still remains an impressive option. And Opera, well -- Opera is still around.

Most of these also-ran programs will likely never reach the heights of Safari or Chrome, let alone Firefox or Internet Explorer. But they present a clear incentive for the top dogs to continue to innovate and improve their usability.

Plus, they haven't resolved that "best browser" argument just yet.