Summer, mosquitoes and vacations could not stop our heroes. Some of them braved the perils of working on the beach to improve the responsiveness of Firefox.

Session Restore

The plans for Session Restore have been overhauled to make way for code that is more e10s-friendly. Our plans to provide a main thread async API are therefore postponed indefinitely, in favor of a content script implementation of state collection. While less asynchronous than earlier prototypes, this implementation should also provide considerable responsiveness benefits, even before we turn on the e10s switch in Firefox. We have also overhauled part of the implementation of Session Restore to ensure that it caches state whenever appropriate, hence removing most of the jank due to state collection. Finally, we have started working on compressing communications between the main thread and the worker to minimize serialization costs. Additional clean-up has been completed, with more under way or is waiting for darker skies before landing.

Places

The titanic work to refactor Places into a non-blocking, off main thread, efficient API, continues. Ongoing works include making backups non-blocking and reducing the I/O cost of backups. We are also preparing a new asynchronous transaction manager for Places. Once this transaction manager has reached a satisfying state, it might be possible to reuse the code (or at least the design) for projects unrelated to Places.

Downloads

The JavaScript downloads API is basically ready. This API is fully asynchronous, JS-friendly and does just about everything off the main thread.

Misc

We are getting close to having a fully off main thread implementation of mozStorage. Partial rewrite/cleanup/modularization of OS.File continues, as well as extending and converting code to Promise.jsm. Also, additional work on porting synchronous code to OS.File.

Side-note

Our work with Async + Responsive has uncovered a number of bugs in the Firefox implementation of Workers and Chrome Workers. This, in itself, is not very surprising, as we are pushing these technologies into a number of places that hadn’t been explored yet. However, the owners of DOM:Workers have been extraordinarily reactive and we would like to thank them. Kudos, guys.