That a bummer! I thought mollies are freshwater fish only LOL.
they fall into the brackish category... um... certain species of fish live where the freshwater river's and streams meet the ocean... the fish after a while swim up stream to lay eggs, they hatch, and once they're older, they go out to the ocean...
molly's are pretty simple to acclimate... they say it takes days, but jose (bgjoe) did it a bunch of times already... he acclimated for a day, sometimes 10hrs tops... a lot of work, but they are pretty cool in reef tanks... also in refugiums, they do a great job cleaning up hair algae and other ugly algaes....
but remember, in this case... a molly in the wild will never encounter a reef... maybe tide pools, but no... so they aren't familiar with the bright warning colors corals and anemones have... poor molly...