here it is at 324 bytes, since your going to end up with scrollbars no matter what, you might as well not worry about document size
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<canvas id=q style=margin:-10><script>for(q.width=q.height=b=3000,m=Math.random,p=[],i=0;i<256;p[i++]=1);setInterval('9Style="rgba(0,0,0,.05)"9Rect(0,0,b,b)9Style="#0F0";p.map(function(v,i){9Text(String.fromCharCode(3e4+m()*33),i*10,v);p[i]=v>758+m()*1e4?0:v+10})'.split(9).join(';q.getContext("2d").fill'),33)</script>