A modded client with any type of mod (be it aether, toomanyitems, better than wolves, etc) cannot be run on the browser. You would need to have a vanilla minecraft.jar. You do this by first making a back up of your current .jar, and doing a force update at the launcher.
You can store this back-up in the bin folder, and minecraft will not read a .jar file if it isn't named minecraft.
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I am the bone of my sword
Steel is my body, and fire is my blood
I have created over a thousand blades
Unknown to death, Nor known to life
Have withstood pain to create many weapons
Yet, those hands will never hold anything
So as I pray, Unlimited Blade Works