Jetpack was introduced in 2013, and by 2014, it was actually usable. It's not clear when and whether Jetpack add-ons will stop working. Mozilla's developer documentation is so confused that you can't tell. WebExtensions and Jetpack are essentially the same functionality with different names.[1]
The trouble with Firefox chasing Google Chrome compatibility is that, once they get there, Google will probably change something so some Google service is essential to an add-on. Like Google did with Android. Then compatible add-ons stop working on Firefox. Nobody runs add-ons on Chrome much, anyway; I have the same add-on on both platforms and its 50:1 Firefox over Chrome. But usage is declining, along with Firefox.
[1] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Co...