Let me start out by saying that I understand the need for something like WebExtensions. A cross browser extension API will be a great thing for the future of browsers. I understand why Mozilla is doing it. What I take issue with is the belief that existing Firefox only add-on developers will jump at the opportunity to use this new API. As far as I’m concerned, the only add-on developers that will benefit from this new API are Chrome developers who will find it much easier to port their extensions to Firefox.

Most Firefox extension developers do it as a hobby. Typically they have an itch about something in Firefox and that write an extension to scratch it. Then they make that extension available to everyone. Over time we all build up a set of extensions that make Firefox behave the way we (and clearly other people) want it to. (Chris Finke is a great example of this.) Every so often something changes in Firefox that breaks one of our extensions. At that point we have to make a decision; it it worth the time and energy to keep this extension going. Sometimes we keep it going, sometimes we give up (hence the ton of dead extensions on AMO). Luckily most of the time Firefox changes don’t break all our extensions, so we usually can keep going. With e10s coming up though, lots of developers have had to make decisions as to whether or not it is worth it to rewrite and some developers have gone through that pain (and it is pain - a lot of pain).

Now developers are being told in the next one to two years they will have to completely rewrite ALL of their add-ons. What are the odds that these hobby add-on developers are going to do that?

Let’s be honest. Availability of APIs isn’t the difficult part of the discussion. Availability of time and energy to even attempt to rewrite all of our add-ons is the problem. And when you add in the fact that Mozilla hasn’t given add-on developers the marketplace we’ve been promised for years (which Chrome has had since day one), you’ll end up with a lot of developers deciding that it’s simply not worth it.

But let's talk availability of APIs. I'll use two of my extensions as examples. Keyword Search accesses the wrappedJSObject of search submissions in order to manipulate the submission. Will there really be an API for that? Or what about the CCK2? Will there really be APIs that allow me to modify the built-in preferences pages including removing pages or controls? Or what about disabling private browsing? Or removing sync? Or removing access to about:config? I doubt it. There are just too many things that extensions do (most of them pretty obscure) to be able to provide an complete API.

I'll watch what goes on and hope that I'm wrong, but I'm not very optimistic.

I will say this, though. It's a great day to be a Chrome developer.

https://mike.kaply.com/2015/08/21/my-take-on-webextensions/