Update: this post was updated to reflect a change in how we determine when Firefox will run in multiprocess mode. Firefox won’t run in multiprocess mode unless add-ons are explicitly declared to be compatible with Multiprocess Firefox. Compatibility shims will be removed earlier than indicated in the previous version of this post. Update 2: we can now confirm that this plan also applies to Firefox
![The Road to Firefox 57 – Compatibility Milestones – Mozilla Add-ons Community Blog](https://cdn-ak-scissors.b.st-hatena.com/image/square/0134428765809fa14253f0831d1fd2b13d96996a/height=288;version=1;width=512/https%3A%2F%2Fblog.mozilla.org%2Faddons%2Ffiles%2F2015%2F09%2Ffoxface_puzzle.jpg)