Chris Double was kind enough to update the SMIL patch on Bug 21642 for Mozilla and then do some builds for me so I wouldn't have to muddle through the build and patch process. I'm ashamed to admit that so far this has been enough of a deterrant that I haven't bothered to try it out, so I'm really glad Chris did this. The best part is that, in doing this, Chris found Firefox crashing on several tests and was able to update the patch to fix these problems.
Anyway, with the patch, a Mozilla trunk nightly gains about 4.5% to their overall SVG score. Put another way, they score 25/116 on the SVG+SMIL animation tests in the Full test suite. While this isn't in the league of current WebKit nightlies (and neither of these platforms are in the league of Opera 9+), it does show that progress could be made on this were it applied to the trunk (once Firefox 3 ships, of course). Does anyone know if this patch means that a Firefox build would pass those SVG+SMIL tests in Acid 3?
[Update: Chris has made the Firefox builds available for download here]
[Update 2008-04-20: Chris' latest build now makes the SMIL score 38/125, though some tests have now regressed.]