Mozilla will shut down support for its Firefox browser running on Windows XP and Windows Vista in 2017, the company said last week.

The exact timing of Firefox’s retirement from those Microsoft operating systems will be determined in the summer, according to a post to a company blog. “We expect to continue to provide security updates for [Windows XP and Windows Vista] users until September 2017,” the firm said. “In mid-2017, user numbers on Windows XP and Vista will be reassessed and a final support end date will be announced.”

Before that, however, Mozilla will automatically migrate Windows XP and Vista users to the Firefox Extended Support Release (ESR), a build-and-release track designed for enterprises and educational organizations. “In approximately March 2017, Windows XP and Vista users will automatically be moved to the ... ESR,” Mozilla said.

ESR builds are regularly updated with security fixes, but do not receive the new features and enhancements that the standard version does. Instead, Firefox ESR remains feature-static for approximately a year, at which time a new ESR is issued. (Microsoft adopted a similar approach with its Windows 10 Long Term Servicing (LTS) Branch, a release track that eschews feature changes for months, or even years.)

Mozilla created the ESR track in 2012 after some customers balked at its scheme to ship a new edition of the browser every six weeks. Firefox ESR 52, slated to ship on March 7, will be what Mozilla moves XP and Vista users to. From that point until Mozilla officially retires Firefox later in the year, XP and Vista users will receive only security updates to the browser.

Microsoft retired Windows XP from support in April 2014, and will do the same to Vista on April 11, 2017. It’s unclear what percentage of Firefox users run the browser on the two aged operating systems, but analytics vendors portray both as minor players. According to metrics company Net Applications, Windows XP powered 8.6% of the world’s personal computers last month, and Vista—one of Microsoft’s biggest OS failures—ran 1.1% of the globe’s PCs.