Android solved that UX issue with Chrome custom tabs (https://developer.chrome.com/multidevice/android/customtabs). It uses a seamless UI exiting the app and everyone uses the up to date browser on the phone.

I only know detail about the iOS equivalent (https://developer.apple.com/reference/safariservices/sfsafar...) but I'm not expecting Facebook to implement it any time soon as it makes it a lot harder to track where a user goes (you can't access that) and/or inject content into the webview.

On the current Android and iOS implementations a user is far less likely to share on, say, Twitter, because they won't have their Twitter login cookies in the Facebook browser. I suspect Facebook is quite happy to keep things that way.

iOS also provides a way to have similar UX using Safari View Controller. https://developer.apple.com/videos/play/wwdc2015/504/

there are problems with both, though. i like to click on something and then give a break, and read later. with CCT, I have to consciously go and click on "open in browser", which doesn't work well for me.

Otherwise, CCT and SVC should be the way to go, still much better than FB. Aside from tracking and all, it doesn't get the niceties of a full blown browser.

iOS has Reading List for this purpose, and SFSafariViewController has a button dedicated for this.

Android also supports a real Firefox, so one needn't trust one's web browsing to the tender mercies of Google.

Great initiative by the Facebook team. Anyone knows if there's a similar framework for Android? (declarative description of the UI, rendering based on immutable models, single data flow, etc)

There's some excellent official documentation on backend writing (http://llvm.org/docs/subsystems.html and http://llvm.org/docs/WritingAnLLVMBackend.html). From my previous experience, it isn't as straightforward as in the docs, but you can use the other backends as reference.