I know you won't like the sound of this, but the only real way right now to get a consistent cross-browser aesthetic in this case, is to use a repeating image.
If it's a simple linear gradient, then you only need it to be 1px wide and as high as the gradient, then make the background colour of the page as the final colour of the gradient so it runs smoothly. This will keep file size tiny.
If you want to reduce gradient bands in your image, use a PNG (not transparency) as I find these to be better suited than JPG's for this purpose.
In Adobe Fireworks, I would export this as a PNG-24.
Good luck.
http://codepen.io/anon/pen/JdEjWm
#gradient {
position: absolute;
width: 100%;
height: 100%;
background: -webkit-gradient(linear, 0% 0%, 0% 100%, from(black), to(white));
background: -webkit-linear-gradient(top, black, white);
background: -moz-linear-gradient(top, black, white);
background: -ms-linear-gradient(top, black, white);
background: -o-linear-gradient(top, black, white);
background: linear-gradient(top, black, white);
}
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