Mozilla, the maker of Firefox, recently accused Microsoft (MSFT 0.39%) of pushing aside rival web browsers in Windows 10 in favor of its new Edge browser. In an open letter to Microsoft CEO Satya Nadella, Mozilla CEO Chris Beard claims that Windows 10 "strips users of their choice by effectively overriding existing user preferences for the web browser and other apps." Beard states that Windows 10 is "designed to throw away" choices about the Internet experience in favor of one that "Microsoft wants them to have."

Microsoft's Edge browser. Source: Microsoft.

Microsoft responded by stating that users can "easily choose the default browser" both during and after the upgrade. Beard acknowledged that those settings existed, but claimed they were "less obvious and more difficult" than they were in previous versions of Windows. Does Mozilla have a point, or is this just a self-serving attempt to vilify Microsoft?

Revisiting the past
To understand Mozilla's beef with Microsoft, we should revisit the company's roots in web browser maker Netscape. Netscape controlled over 90% of the web browser market back in the mid-1990s, but it was eventually crushed by Microsoft's Internet Explorer. In 1998, AOL acquired Netscape, and a small group of Netscape's employees formed Mozilla.

Between 1998 and 2001, the U.S. Department of Justice sued Microsoft over alleged antitrust violations. While Netscape wasn't a plaintiff, the central argument against Microsoft was that it unfairly leveraged its strength in operating systems by bundling IE into Windows. Since every new Windows user had a copy of IE, the market for rival browsers faded away.

Microsoft was subsequently ordered to unbundle IE from Windows. But after those terms expired in 2011, Microsoft picked up right where it left off by bundling IE with new copies of Windows 8.

Crushed between two giants
However, Google (GOOG 1.99%) (GOOGL 2.02%) -- not Microsoft -- is Mozilla's biggest competitor today. Back in 2010, Firefox claimed 23.5% of the desktop browser market, compared to 59% for IE and 2% for Chrome, according to Net Market Share.

But over the past five years, Google Chrome took a huge bite out of Firefox's market share. By July 2015, Firefox only controlled 12% of the market, compared to 28% for Chrome and 53% for IE. The mobile version of Firefox accounts for less than 1% of all browsers worldwide, compared to 33% for Chrome.

Firefox is being crushed because it, like Netscape, isn't part of a major OS ecosystem. As long as most PCs run Windows and most mobile devices run Android, Microsoft and Google will have a big advantage in the web browser market. As Microsoft and Google expand their ecosystems by synchronizing browsing data across multiple platforms, alternative web browsers like Firefox could be rendered obsolete.

That's why Firefox introduced Firefox OS, a Linux-based OS for mobile devices and smart TVs, two years ago. But in a world split between Android and iOS devices, it remains an overlooked, niche OS.

Firefox OS for smartphones. Source: Mozilla.

Why Mozilla's days are numbered
Most of Mozilla's money comes from a search deal with Google. Whenever a user enters a Google search query into Firefox's search bar, Google shares those ad revenues with Mozilla. In 2013 (its most recently reported year), those payments accounted for 90% of Mozilla's top line. As Firefox's user base shrinks, those payments will inevitably decline.

Meanwhile, Microsoft's Windows 10 launch could unify mobile devices, PCs, and even video game consoles under a single OS with a unified app store. In this ecosystem, Edge and Cortana play key roles in synchronizing user data across multiple platforms. Therefore, Microsoft would certainly prefer that users use Edge instead of Firefox, Opera, or Chrome.

Mozilla claims that Microsoft is "overriding user preferences," but the sad fact is that stand-alone web browsers are becoming redundant in Microsoft and Google's ecosystems. Users on Windows 10 PCs will likely prefer to use Edge instead of Firefox, simply because it complements other new features and syncs data more easily across multiple devices.

Is Mozilla the next Netscape?
Looking ahead, Mozilla seems doomed to follow the footsteps of Netscape. Just like Netscape in its twilight years, Mozilla is complaining that Microsoft has an unfair advantage.

But unlike Netscape, this "advantage" probably won't lead to another lengthy antitrust battle, since the Windows 10 upgrade doesn't forcibly uninstall rival browsers. Instead, Firefox could eventually disappear as first-party browsers become inseparable from leading operating systems like Windows and Android.