On February 25, Mozilla introduced new terms of use (ToU) for Firefox that included, among other things, the following: “When you upload or input information through Firefox, you hereby grant us a nonexclusive, royalty-free, worldwide license to use that information to help you navigate, experience, and interact with online content as you indicate with your use of Firefox.” A hornet’s nest of uproar followed, and Mozilla has since rewritten that paragraph in an attempt to clarify it, but there are still concerns within the open-source, privacy, and web communities.

Firefox Is Still MPL … Just Not For Most Users

Mozilla has not changed the license terms for Firefox source code. That’s still distributed under the Mozilla Public License (MPL). The ToU apply only to “the ‘Executable Code’ version” of Firefox from Mozilla. Mozilla currently provides a compiled version of Firefox to Linux distributions such as Debian and Ubuntu, however, and most Windows users who download Firefox get it from Mozilla. Only a few Linux distributions like Gentoo offer a relatively easy way for users to compile Firefox manually.

Earlier Mozilla efforts to add services already resulted in forks of Firefox like LibreWolf and Zen. It seems likely that Firefox users who are concerned about Mozilla’s use of their data will migrate to those or similar browsers. Linux distributions that want to ship Firefox without code that sends data back to Mozilla will run into trademark issues.

Firefox Loses Its Niche

In the early days of data deprecation, web browsers were in a footrace to win users over by touting their privacy-protecting capabilities. Firefox was an active participant with its Enhanced Tracking Protection, which blocks cross-site tracking and is enabled by default for all users. Google’s never-ending dance around third-party cookies added fuel to the competitive fire.

Updates to the terms of service hit privacy-savvy consumers particularly hard: Firefox deleted its previously strong stance on privacy. In a Q&A section, Mozilla previously asked, “Does Firefox sell your personal data?” To which it responded, “Nope. Never have, never will. And we protect you from many of the advertisers who do. Firefox products are designed to protect your privacy. That’s a promise.” All of this is gone. Some users understandably see it as a promise broken.

The update also raises questions at a broader enterprise level. Businesses must be aware that by using Firefox, even only for internal websites, their users may be sending information to Mozilla under a royalty-free license. CIOs and CISOs will need to weigh the benefits of Firefox against the risks that corporate data may become visible to Mozilla or its partners.

Firefox finds itself in a very difficult position in determining how to retain its user base of privacy-minded consumers, as well as how to acquire new users by differentiating from the big tech-owned default browsers without big tech resources.

The 2% Cliff Will Trigger A Negative Feedback Loop

Advocates of browser heterogeneity see trouble brewing. Firefox has always had a smaller user base: According to W3Counter, Firefox had a 4% browser share in January 2025; in October 2024, Statcounter put it at 2.9%. Many web developers, including those who use the US government’s design standards or the UK government’s advice on designing for different browsers, use 2% as the minimum browser adoption required for support. Every website will be different, but organizations will be watching their analytics. Firefox has already fallen below this threshold for the yearly statistics on analytics.usa.gov, which is the measure of browser share used by US government sites. With a further exodus of Firefox users:

  • Current Firefox users will become more frustrated. Already, there are many sites that don’t work properly under Firefox, and that number is likely to grow. Existing Firefox users will eventually give up and move to alternatives based on Chromium or WebKit in a slow drip of attrition.
  • Web developers will shelve Firefox testing. Many web developers have a fond regard for Firefox and may voluntarily work to support it, but they will face the reality that businesses won’t pay for testing against Firefox browsers. This will create a reinforcing cycle of sites that don’t render or act properly in Firefox, creating negative experiences for users, causing them to experiment with other browsers, and further eroding Firefox’s market share.
  • Marketers and advertisers will get some reprieve — for now. Firefox’s Enhanced Tracking Protection makes tracking Firefox users and their responses to ads very difficult for marketers. If those users shift to Chrome or other tracking-friendly browsers, marketers may feel a false sense of relief that their granular metrics aren’t dead after all. But as marketers have learned, companies like Google and Apple wield a lot of influence and aren’t afraid of making unilateral decisions that directly impact marketing, so this may be a reprieve in the data deprecation story, but marketers, don’t rest on your laurels.
  • Web testing vendors will reduce Firefox support. It’s a point of pride among many testing vendors to support as broad an array of user agents as possible, but if Firefox falls from a first-class citizen to a checkbox, the depth of platform support for Firefox will decrease — fewer back-level versions will be available to test.

Mozilla Has Been Squeezed — Is This The “Pop”?

We recognize that Mozilla needs to make a profit, and its largest revenue source — payments from Google to make it the default search engine — is at risk after the US Department of Justice ruled that Google Search is an illegal monopoly. The introduction of the new ToU feels like a further erosion of Firefox’s previously privacy-friendly stance. It’s hard to see how this move increases Firefox’s market share or appeals to its user base. A cynic might say that it’s a last-ditch attempt at profitability for Firefox. No matter what, it is a cautionary tale about running legal changes past a few of your existing users to see how they land.