@Stuart ********
Mae Sot just reopened to Thais and Burmese not sure about foreigners. Up until today, Burmese needed special permission to cross at land borders and only as repatriates - Thailand did not permit entry except for traders and drivers delivering goods at specific checkpoints. For ordinary travelers, today marks the first day borders are open.
However, it's reported that Thais have been allowed to visit some islands off the southernmost part of Myanmar since at least early December. Foreigners are not permitted at present.