To ease the development of cross-viewer SVG content I have started the SVG devbar, a collection of handy bookmark(let)s and a non-blank document to start coding SVG with. Both are meant to prevent and pinpoint bugs in your code and work around viewer shortcomings.
Though this combination has a few very simple but handy functions already, it is in its very early stages. Several planned features are not yet implemented. Next to just bookmarklets, it might also grow into a rich Firefox SVG extension for example.
Feedback is very welcome (e.g. feature requests, bugreports, offers of help).