WebExtensions SDK will be it

The big cheeses of the Mozarella foundation will ship Firefox 57 as the first version of its browser that will not support legacy Firefox add-ons.

Might actually be useful

A new preview of build (14342) of Windows 10 has zipped out to Insiders on the Fast Ring, and this finally sees extensions become fully functional and easy to install in Microsoft Edge.

Requires iOS 8 and above

Over the past seven and a half years since the App Store launched in July 2008, Apple’s mobile application market has blossomed from a size of just 500 applications at launch to more than 1.5 million as of last month. Unfortunately, even with all of these apps readily available, the company has been reluctantly strict in allowing developers the ability to change application functionality with their own third-party enhancements. Until last summer, the process was mostly restricted to jailbroken iOS devices and there have been few app tweaks available for non-jailbroken devices, until now.