Firefox uses GTK to draw native-looking widgets. Basically, Gecko passes an X11 pixmap to GTK2 the latter draws the buttons/scroll bars/etc. into it with xrender. This means that Firefox either has to do all of the rendering with xrender and pixmaps, or do an expensive read-back of the native widgets from the pixmap and draw other web content into whatever kind of surface it wants. The thing is, we really really want to move away from xrender. GTK3 has a slightly different API for this and can draw native widgets into any kind of surface that can be wrapped in a cairo context. So for Firefox, the most important part of moving to GTK3 is the removal of this dependency to X11 and xrender. Chrome (as far as I know) doesn't do native-looking widgets (and to be honest I would be happier if Firefox didn't either), so moving to GTK3 is not that big of a deal for Chrome because it doesn't use the GTK nearly as much as Fireox does.

I don't really use chrome. If the widgets don't look native that's fine, but do they behave natively? If they're not drawn by gtk, do the standard keybindings work if they've been changed from gtk's defaults. If not that would be quite infuriating to use.

It's a real shame chrome moved away from GTK. Aura is probably fine for many use cases but it does weird stuff on multi-monitor setups (drawing artifacts and windows jumping around).

Aura really doesn't like my xmonad setup. Chrome doesn't like it at all either. If I lose focus of the chrome window due to a Panel coming up (undocked window), chrome won't regain focus and I can't type anywhere and I have to SIGTERM it to make it work again. quite annoying.

I've had issues with chrome/xmonad not regaining focus properly that were fixed by adding the code mentioned in the 'usage' section of this page: http://xmonad.org/xmonad-docs/xmonad-contrib/XMonad-Hooks-Ew...

Not sure if that'll help you with your specific program, but it might.

As an i3wm user, sometimes, but not always, after resuming from sleep, chrome puts context menues (and only context menues) on my other screen, so I wholeheartedly agree that Aura and multi-monitor (tiling?) setups have some issues.

I wonder if the difference in decision here has to do with Firefox having its own Long Term Support version. So people needing GTK2 on say Ubuntu LTS can use Firefox LTS for that, and latest Firefox is more free to focus on GTK3.

Firefox' LTS (called ESR) [1] only has one year of support in it (as opposed to default six weeks).

[1] https://www.mozilla.org/en-US/firefox/organizations/faq/

So Chrome has its own GUI toolkit?

Yes: http://dev.chromium.org/developers/design-documents/aura

Are there any other projects, Google or otherwise, that's using Aura?

No, because it is horribly broken in many situations: On linux, context menus often end up on a different monitor than the window, on windows, Aura can’t render text readable at all, etc.

Still when I upload a file, I get the native file selection box.

Also, the "use system title bar and borders" option (when right-clicking on the topmost bar) feels a bit like a hack, but I guess it is the best solution to get rid of that extra top window decoration space on most OSes.

Some discussion here https://code.google.com/p/chromium/issues/detail?id=79722