I think everyone knows about how companies use stored flash objects as cookies, but now something even more devious. A new cookie on firefox that can never be erased. the DomStorage cookie. Just a matter of time before ebay et al use it on you. So disable it now.
Here's how to disable it
Managing Mozilla/Firefox DOM Storage Privacy. If you use a Mozilla browser, you can disable DOM Storage pseudo-cookies by typing about:config into the URL bar. That will bring up an extensive list of internal browser configuration options. Type "storage" into the filter box, and press return. You should see an option called dom.storage.enabled. Change it to "false".
also to check out the cookies on your flash player go here
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Even if you do run a Mac platform you should STILL use different user accounts on your computer.
I have 5 Mac's in my house. 3 iMacs and 2 Powerbooks.
I use different computer user accounts for ALL my eBay/Paypal needs.
This keeps ALL cookies separate.
It has nothing to do with Mac VS PC
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Once you go Mac you will never go back