<canvas> is not a standard W3C element and I had never heard of it but your mozilla link says it is part of the WHAT html5 thing. The link also says Safari supports it but I would have no way of helping with this. Personally, I consider the WHAT group to be a bit of a rogue operation but I also confess that I pay no attention to them so how legitimate their actions are may be transparent to me.
It's strange that it doesn't work on Safari, as Apple are apparently the ones that invented canvas.
The reason I chose canvas was that it seemed like it had the most support (FF2, Opera 9, Safari? & IE with extra javascript).
I might look into the Dojo javascript library as that is supposed to be able to draw vector images (I was hoping to avoid having to load a big library every time the page is accessed).