Firefox 1.5 is not even out yet, but right now there are some pretty significant pieces of work going on to update the SVG functionality available (I'm assuming these patches will not make it into Firefox 1.5, but I could be wrong). In fact patches exist for:
As soon as I get some time I'll try to remember how to build Firefox (last time I tried there were some errors), get some of these patches, apply them, and test it out. Should be fun...