Question: why can not sign in two hotmail acount at the same time using firefox? what doese this mean also: "cookies are used to personalize Web search engines, to allow users to participate in WWW-wide contests (but only once!)" thank you so much

Answer: Hotmail stores a file (cookie) on your PC to identify the user  just like Yahoo does so the webpage and information such as email is current for that user. Two accounts cannot be active at the same time on the same PC.
This question from the Yahoo Q&A forum is categorized in the topic: Science & Mathematics