Steps:
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1. Turn on 2 internet explorers (or mozilla firefox or watever)
2. Go to runescape.com on both of them
3. Then, on one of them go to a world like u normaly would
4. On the other one press play now, then move down to the Java options tab. Select the bottom one.
5. Then click low detail and on the world page click the world the other internet browser is on
Pretty sure this should work unless they fixed it.
Or go on one account with Rsbot and another without.