Note: Starting in Firefox 57, which will be released in November 2017, only add-ons built with this new technology will work in Firefox. These are indicated by the “Compatible with Firefox 57+” label on addons.mozilla.org (AMO). Add-ons built with the old technology are labeled “Legacy” on the about:addons tab. If an add-on does not have the "Compatible with 57+" label, or has the "Legacy" label, the developer may be in the process of transitioning to the new technology. You may find developer contact information on the right side of the add-on listing on AMO.