Firefox not anti-aliasing scaled background svg

Give the outer <svg> element in the svg file (sophie-conran.svg) a width and height of 100%.

What happens is that the svg image is rasterised at the width and height you give it i.e. 1000px x 350px and that bitmap is then converted to the required size. If you make the width and height percentages then the bitmap is created at final size and there's no bitmap scaling.

Update:

This is all moot with Firefox 24 and beyond though, you can do what you like and it will always work properly i.e. without pixellation.