Password Protected HTHL5 LocalStorage Security?

I've just started my venture into HTML5 localStorage. I now have a javascript my server sends to those who visit my ip address. I store all their data using localStorage. I have a few security questions regarding the HTML5 localStorage situation:

1. Can a script that did not create the local storage retrieve/modify the localStorage of another script just by guessing the key maliciously or unintentionally?

2. Can another script use the clear() method to remove my scripts data? Edit: I just tried this myself. And, yes, I deleted my data, all of it with clear() using a different script. Is there any way to prevent this? Is it only my end that will be able to do it or could I load a script from a site has a hidden clear() method and destory all other javascript apps data?

3. If item (2) is true, any ideas on how to protect my scripts data for the user from the clear method?

4. if item (2) is false, cool, my first idea is to create a uniqnue string random string and ask the user to creat a password to encrpt that string and just use that string with enumeration added to it for the keys.

5. Does anyone know where localData is stored? Is it encrypted already, in plain text, in well-known or hidden location?