TenFourFox 45.3.0b2 available

TenFourFox 45.3 beta 2 is now available (downloads, hashes, release notes). The issue with video frame skipping gone awry seems to be due to Mozilla's MediaSource implementation, which is (charitably) somewhat incomplete on 45 and not well-tested on systems of our, uh, vintage. Because audio is easier to decode than video the audio decoder thread will already have a speed advantage, but in addition the video decoder thread appears to only adjust itself for the time spent in decoding, not the time spent pushing the frames to the compositor or blitting them to the screen (which are also fairly costly in our software-rendered world). A frame that's simple to decode but requires a lot of painting will cause the video thread to get further and further behind queueing frames that the compositor can't keep up with. Even if you keep skipping keyframes, you'll end up more than one keyframe behind and you'll never catch up, and when this occurs the threads irrevocably go out of sync. The point at which this happens for many videos is almost deterministic and correlates well with time spent in compositing and drawing; you can invariably trigger it by putting the video into full screen mode which dramatically increases the effort required to paint frames. In a few cases the system would just give up and refuse to play further (hitting an assertion in debug mode).

After a few days of screaming and angry hacking (backporting some future bug fixes, new code for dumping frames that can never be rendered, throwing out the entire queue if we get so far behind we'll never reasonably catch up) I finally got the G5 to be able to hold its own in Reduced Performance but it's just too far beyond the G4 systems to do so. That's a shame since when it does work it appears to work pretty well. Nevertheless, for release I've decided to turn MediaSource off entirely and it now renders mostly using the same pipeline as 38 (fortunately, the other improvements to pixel pushing do make this quicker than 38 was; my iBook G4/1.33 now maintains a decent frame rate for most standard definition videos in Automatic Performance mode). If the feature becomes necessary in the future I'm afraid it will only be a reasonable option for G5 machines in its current state, but at least right now disabling MediaSource is functional and sufficient for the time being to get video support back to where it was.

The issue with the Amazon Music player is not related to or fixed by this change, however. I'm thinking that I'll have to redo our minimp3 support as a platform MP3 decoder so that we use more of Mozilla's internal media machinery; that refactoring is not likely to occur by release, so we'll ship with the old decoder that works most other places and deal with it in a future update. I don't consider this a showstopper unless it's affecting other sites.

Other changes in 45.3 beta 2 are some additional performance improvements. Most of these are trivial (including some minor changes to branching and proper use of single-precision math in the JIT), but two are of note, one backport that reduces the amount of allocation with scrolling and improves overall scrolling performance as a result, and another one I backported that reduces the amount of scanning required for garbage collection (by making garbage collection only run in the "dirty" zones after cycle collection instead of effectively globally). You'll notice that RAM use is a bit higher at any given moment, but it does go back down, and the browser has many fewer random pauses now because much less work needs to be done. Additionally in this beta unsigned extensions should work again and the update source is now set to the XML for 45. One final issue I want to repair before launch is largely server-side, hooking up the TenFourFox help button redirector to use Mozilla's knowledge base articles where appropriate instead of simply redirecting to our admittedly very sparse set of help documents on Tenderapp. This work item won't need a browser update; it will "just work" when I finish the code on Floodgap's server.

At this point barring some other major crisis I consider the browser shippable as 45.4 on time on 13 September, with Amazon Music being the highest priority issue to fix, and then we can start talking about what features we will add while we remain on feature parity. There will also be a subsequent point release of TenFourFoxBox to update foxboxes for new features in 45; stay tuned for that. Meanwhile, we could sure use your help on a couple other things:

• Right now, our localized languages for the 45 launch are German, Spanish, French and Japanese, with an Italian translation in progress. We can launch with that, but we're losing a few languages there we had with 38. You can help.

• Even minor releases of the browser get a small bump in support tickets on Tenderapp; a major release (such as 31 to 38, and now 38 to 45) generally brings lots of things out of the woodwork that we've never seen during the beta cycle. Most of these reports are spurious, but sometimes serious bugs have been uncovered even though they looked obviously bogus at first glance, and all of them need to be triaged regardless. If you're a reasonably adept user and you've got a decent understanding of how the browser works, help us help your fellow users by being a volunteer on Tenderapp. There's no minimum time commitment required; any help you can offer is appreciated, even if just temporary. Right now it's just Chris Trusch and me trying to field these reports, which is unsatisfactory to cover all of them (Theo used to but we haven't seen him in awhile). If you'd like to help, post in the comments and we'll make you a "blue name" on Tenderapp too.

That's it for now. See what you think.