Mozilla announced today plans to remove all Firefox legacy add-ons from the official Mozilla add-ons portal later this year, in early October.

The move comes after Mozilla updated the Firefox core to use a new add-ons system based on the Chrome-compatible WebExtensions API.

This new add-ons API replaced Firefox's old XUL-based add-ons API in November 2017, with the release of Firefox 57.

No more Firefox versions that support legacy add-ons

All Firefox legacy add-ons stopped working in Firefox 57, but Mozilla continued to support them in the Firefox Extended Support Release (ESR) 52 branch.

Support for Firefox ESR 52 will end on September 5, in two weeks, meaning there won't be any official Firefox version that supports legacy add-ons anymore.

Mozilla said today that following this date, it plans to start the process of disabling legacy add-on versions on its add-ons portal located at addons.mozilla.org (also known as the AMO).

"On September 6, 2018, submissions for new legacy add-on versions will be disabled," said Caitlin Neiman, Add-ons Community Manager at Mozilla.

"All legacy add-on versions will be disabled in early October, 2018. Once this happens, users will no longer be able to find [extensions] on AMO," she added.

Old legacy add-ons can be revived by original developers

The only way to revive these older legacy add-ons is if their original developers port the legacy add-ons to the new WebExtensions API.

"Once a new version is submitted to AMO, users who have installed the legacy version will automatically receive the update and the add-on’s listing will appear in the gallery," Neiman said.