Mozilla today announced that it will completely drop support for Firefox on Windows XP and Windows Vista in June 2018. Firefox users on those two platforms can expect security updates until then but should make an effort to upgrade Windows sooner rather than later.

When Mozilla released Firefox 53 in April 2017, it no longer supported Windows XP and Windows Vista. Instead, XP and Vista users were moved to the Firefox Extended Support Release (ESR). Firefox ESR is designed for schools, universities, businesses, and others who need help with mass deployments.

Mozilla promised last December to reassess user numbers in mid-2017 and announce a final support end date for the two operating systems. That time, while a bit delayed, has now come.

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.

Mozilla correctly notes that “unsupported operating systems receive no security updates, have known exploits, and are dangerous for you to use” and it “strongly encourages” users to “upgrade to a version of Windows that is supported by Microsoft.”

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 was pulled on April 11, 2017. Mozilla thus supported XP and Vista even longer than Microsoft did.

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.

Since neither IE nor Chrome are options, many are using Firefox. That’s likely why Mozilla kept support around for so long — it’s the best option for hundreds of millions of users.

Last month, XP had less than 6 percent market share, per Net Applications. In fact, XP and Vista combined held 6.12 percent of the pie — not an insignificant 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 terrible security choice.