I upgraded to Firefox 57 only to find all 4 of my extensions missing... I can live without others, but being without NoScript felt like walking on streets naked. So the first thing I did was downgrade to Firefox ESR, then I started looking for alternatives. Turns out that uMatrix fills this role perfectly (for me of course). Not only can I block/allow JS, CSS and similar resources, but I can do it based on domain / 3rd party domain matrix... Nice, I always hated that when I allow `gstatic.com` in NoScript for some domain it is allowed globally (for all domains). I will test uMatrix for a few more days just to see if I feel comfortable without NoScript, then I'll upgrade back to FF 57. It looks like this might have a silver lining after all. :)
(for the record: I hate it that they broke compatibility with older extensions, and I hate that they changed UI, but if that gives FF greater market share, then I'm all for it)
Killing the old extension API is a painful, but important, step.
From a security standpoint, WebExtensions are a lot better, since they are sandboxed and require explicit permissions to be granted for many things.
From a developer standpoint, they are easier to deal with, being JavaScript, and since Chrome and Edge support similar APIs, developers will no longer need multiple codebases to support their extensions on multiple browsers.
They also work better with a highly concurrent browser. They use asynchronous APIs that don't directly call into browser APIs. FFs old extensions were known for leaking memory, which is a lot less of an issue with WebExtensions.
Compatibility is another huge thing. With old Firefox extensions, compatibility was just an extension author saying, "Yep, the APIs still work the way I'm using them." They often broke in subtle ways and you could get them partially working by overriding the versions supported in the extension manifest. Not so great imo. WebExtension APIs are more or less like JavaScript APIs and compatibility is mostly going to be limited by support for capabilities. Like, I'm sure Firefox does not support the USB API that Chrome does.
There's so much to be gained from getting rid of the old extension system for concurrency, extension compatibility, and the health of the ecosystem and individual browser installations. Many will be angry and stick to ESRs and others will be mildly upset but I think in the long run this will have been one of the better Mozilla decisions that make Quantum a success.
> There's so much to be gained from getting rid of the old extension system for concurrency, extension compatibility, and the health of the ecosystem and individual browser installations.
I personally think that while it's clearly great for security and possibly good for Firefox in general, it's also terrible for the extension ecosystem. The set of possible extensions is being reduced from "literally anything computable" to "what the API supports." Sure, (some) popular extensions are basically being grandfathered in by having APIs added just for them, but that doesn't help the extensions that aren't written yet and will now never be written.
Essentially, a major selling point of Firefox has been sacrificed in the hope that the increased security, better perf, and greater development velocity leads to greater marketshare. Well, I hope so, but I think the jury will be out on that for a while.
Other than that, Quantum seems great. I did lose all my tabs when it updated (boo - that's never happened before), and I think the whole-window-width address bar dropdown is bizarre and ugly, but other than that it's great. I suppose the only long-term concern is that default merger of the address bar and search bar - configurable options have a habit of eventually being dropped, and I think a world of omnibars is less usable and less privacy-conscious.
After reading these comments, I basically don't want to upgrade. I've been running Classic Theme Restorer for years to get rid of whatever the latest craze in GUI design is. I like my address bar for addresses and my search bar for searches. I love my tree style tabs. I like having a fair amount of control over my browser.
For a few years now, I've had the feeling that Firefox was actively trying to get rid of me as a user. With every new version, the user is less and less in control. It claims to be privacy-conscious, but runs Google Analytics. It tries to gather data behind my back. It's missing so many switches and toggles that I had to install a Privacy Settings extension simply to make the thing behave.