Mozilla today announced that it will end Firefox support for OS X 10.6 Snow Leopard, OS X 10.7 Lion, and OS X 10.8 Mountain Lion in August 2016. Unlike Google, which also dropped Windows XP and Vista support, Mozilla seems to be sticking to only removing support for old Macs.

This means Mozilla will provide regular Firefox updates and security patches for Mac users on these operating systems for four more months. After that, the browser will still work, but it will be stuck on the last version released in August.

Mozilla also offers a Firefox version called Extended Support Release (ESR) for schools, universities, businesses, and others who need help with mass deployments. Firefox ESR releases are maintained for one year, and so Mozilla will continue to support it on OS X 10.6, 10.7, and 10.8 “until mid-2017.” Firefox ESR 45 will be the last version that supports these old OS X versions.

Mozilla correctly notes that “all three of these versions are no longer supported by Apple” and that “unsupported operating systems receive no security updates, have known exploits, and are dangerous for you to use.” If you want to continue getting Firefox updates, the company thus recommends upgrading your Mac.

It’s unfortunate that Mozilla is not doing the same with old Windows versions. 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. Mozilla is thus going out of its way to support XP for additional years, even longer than Microsoft.

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 users thus choose to use third-party browsers.

With Chrome no longer an option, many are likely going with Firefox.

Last month, XP still had about 11 percent market share, according to Net Applications. Vista had 1.41 percent market share, and the three old OS X versions had a combined 0.83 percent.

So if you’re wondering why exactly Mozilla keeps supporting Firefox on Windows XP and Vista, the numbers tell the real story. There are hundreds of millions using the browser on the ancient operating systems, and Mozilla would rather have those users than lose them.

But like Google before it, Mozilla is not helping these users by not encouraging them to upgrade. Even with an up-to-date browser, using Windows XP and Vista is simply a poor security choice.