-It is common after a brachioplasty (arm lift) operation to have a lot of swelling in the arms that can take weeks to fully resolve. This could be the reason that your arms feel firm. -Massage, time, and keeping the arms elevated as much as possible, all seems to help with this swelling. -Definitely, check with your plastic surgeon and have him/her examine your arms as you may find this reassuring as well. Take care!
Congratulations on having undergone the arm lifting surgery. Unfortunately, without more information in your question, it is not possible to provide you with specific thoughts/advice. If you have specific concerns about your postoperative course or results you will be better off addressing these concerns with your plastic surgeon in person. Best wishes.