Because the is the American currency
Not for official government services. You can go to a bank to exchange currency.
Yes you can but just convert it into lebanese money to be safe..You can buy Lebanese money in the UK - try Thomas Exchange UK Limited in London - visit their shop in person or order by post.Their web...
Some retailers accept US dollars though not all.
No. They use the Mexican Peso (MXP). However in or around tourist areas, many street vendors and establishments accept US Dollars.