Mozilla today announced that it will continue to support Firefox for Windows XP and Windows Vista until September 2017. In March 2017, XP and Vista users will automatically be moved to the Firefox Extended Support Release (ESR), and in mid-2017 the company will reassess user numbers to announce a final support end date for the two operating systems.

Firefox ESR is a version designed for schools, universities, businesses, and others who need help with mass deployments. Firefox ESR releases are maintained for one year.

In August 2016, Mozilla dropped Firefox support for OS X 10.6 Snow Leopard, OS X 10.7 Lion, and OS X 10.8 Mountain Lion. Unlike Google, which in addition to old OS X releases also dropped Windows XP and Vista support, Mozilla decided to keep supporting older versions of Windows.

This means Mozilla will provide regular Firefox security patches for XP and Vista users for nine more months. After that, it may continue for a few more months, but eventually the browser won’t get new versions on those operating systems.

Mozilla correctly notes that “unsupported operating systems receive no security updates, have known exploits, and are dangerous for you to use.” The company also tells enterprises that September 2017 should be considered the support end date for planning purposes and “strongly recommends” that all users “upgrade to a version of Windows that is supported by Microsoft.”

And yet Mozilla is taking its sweet time. Keep in mind that Microsoft retired Mainstream Support for Windows XP on April 14, 2009 and then pulled Extended Support for the operating system on April 8, 2014. Mainstream Support for Vista ended on April 10, 2012 and Extended Support will be pulled on April 11, 2017. Mozilla is thus going out of its way to support XP for additional years, and Vista for a few months, even longer than Microsoft in both cases.

Windows XP users cannot upgrade to newer versions of Microsoft’s browser: IE8 is the latest version they can install. IE9 is only available for Windows Vista and Windows 7, while IE10 and IE11 are only for Windows 7 and Windows 8. Many XP and Vista users thus choose to use third-party browsers.

With Chrome no longer an option, many are likely using Firefox. That’s probably why Mozilla is keeping support around for long — it’s the best option for hundreds of millions of users.

Last month, XP had less than 10 percent market share, per Net Applications. In fact, XP and Vista combined held 9.73 percent of the pie — a significant number to be sure, but one that shows people need to be encouraged to get off ancient operating systems. Even with an up-to-date browser, using XP and Vista is simply a poor security choice.