If you've been living in a cave with D.B. Cooper counting his inflation-ravaged ill-gotten gains over the weekend, you may have missed the news that Australis landed in Firefox slated for Fx28, and appears to be sticking (I didn't make this announcement on the day of because I suspected it would be backed out for bustage, and it looks like my guess was wrong). Australis, of course, is Mozilla's new interface for Firefox, radically replacing the current appearance which has remained relatively unchanged since a minor facelift and modifications for Firefox 4.
The response has been decidedly mixed at best. One particularly dire estimate from Mozilla's own feedback system says only 20% of Firefox nightly users like the changes, though this is a small sample of apparently really p*ssed off people, and may reflect bugs or add-on incompatibility along with the differences in appearance. Still, these are the users most likely to enjoy new shiny and least likely to be offended by change purely for being change; they're on the nightly build branch, after all, so this early feedback bodes poorly. Australis' most controversial changes include larger icons and larger tabs, no more small icons mode, removal of certain customization options like hiding the navigation bar, and completely dispensing with the add-on bar altogether (marked for death in Fx4 but restored as an option after fierce complaints; it now appears that the stay of execution has expired). Oh, and tabs on the bottom? That's been marginalized for some time and now it's gone too.
Irked users are, of course, fighting back (paradoxically demonstrating Mozilla's continued high level of customizability even post-Australis); there is already an add-on to restore most of what was lost, and the most incensed Nightly users are moving over to the holly branch, which is a temporary stopgap branch of Fx28 using the previous chrome created by Mozilla in case a backout was required. (It is not likely to persist much longer now.) At least one custom Firefox rebuilder, Pale Moon, is making their intentional omission of Australis a selling point.
Australis just adds to our porting woes. Remember, we are committed to 10.4 support; there will not be a 10.5-only TenFourFox, at least not from me. Although initially I had optimism that the technical issues could be worked around, we already have at least one glitch due to the underlying widget changes (issue 247) and future changes will likely make this worse. There are also new dependencies on components of the Objective-C 2.0 runtime (10.5+) which probably can't be effectively implemented for 10.4.
Australis also has practical considerations for our older machines. Its performance is judged to be similar to old Firefox, but this is on systems with hardware acceleration; software is now a fallback, and we render entirely in software. The larger tabs and icons have a big impact on machines limited to fixed resolutions, particularly the iBooks and iMacs: this iMac G4 I'm typing on has only a 1024x768 display, and tabs this large will impair its useability and reduce the content area. If you want to get an idea of the magnitude of this effect, load up Tenfourbird, the tabs implementation of which Australis is approximately based upon. (By the way, this is not the fault of our Anonymous Builder in the Land of the Rising Sun; this is the way Thunderbird ships, and as an avid user of Tenfourbird for Usenet, we are glad to have him in the 10.4Fx ecosystem. Arigatoo gozaimashita.) Look at the swooping tabs in Tenfourbird. Those are, roughly, the size of the Australis tabs. See how much more real estate they take up? While you're at it, increase the size of the icons if you're in small icons mode, maybe throw a few more icons up there (that's where your addons will go). What does that do for your productivity?
It's not a good day.