Mozilla last week shut down Firefox's support for Windows XP and Windows Vista, ending browser security updates for the outdated operating systems.

"It required effort, and it required devoting resources to supporting XP well after Microsoft stopped doing so," Chris Hutten-Czapski, a Firefox engineer, said in a Sept. 5 post to his personal blog. "It meant we couldn't do other things, since we were busy with XP."

Support for the two past-expiration-date OSes - Microsoft dropped Windows XP in April 2014, Vista in April 2017 - ended with Firefox ESR 52.9, which was released June 26. That version was supplanted by Firefox ESR 60.2 on Sept. 4.

Firefox ESR, for "Extended Support Release," is a version Mozilla issues to customers - primarily business users - who value stability over sexy new features. Unlike the standard Firefox, each ESR version receives only security updates during its tenure. About once a year, Mozilla replaces the existing ESR with the then-current Firefox, then maintains both the old and new ESR versions during a 12-week overlap period. Firefox ESR 52's overlap with ESR 60 began May 7, when the latter launched, and ended Sept. 4, when that date's security patches were not provided for the former.

Mozilla automatically moved Firefox users still running Windows XP or Vista to ESR 32 in March 2017; they have been browsing with that version since.

Other browser makers - notably Google and Microsoft - erased Windows XP and Windows Vista from their support lists some time ago. Chrome scratched XP in late 2015, for example, while Internet Explorer (IE) did the same in April 2014. With Firefox's pull-the-plug move, the only Top 5 browser still supporting the ancient OS is Opera. The Norway-based browser quit adding features to the last XP- and Vista-compatible version, which was 2016's 36, but has continued to issue security updates for that edition.