Ideas
+1
Favorite import tool for FA
it will basicly try to migrate the favorites of your user from site like FA to FurrryNetwork by indexing the images found and comparing them to what the site already has by either hash or tags.
Customer support service by UserEcho
I wouldn't imagine this to be a very easy thing to make. Users can often have thousands of favorites and scraping Furaffinity for all that information and finding matches probably isn't ideal.
I did just think of another way that could produce decent results. When users use the gallery import tool FN could index the submission id the image was imported from and then FN would only need to scrape the gallery pages and find the imported submissions. This wouldn't cover submissions uploaded directly to FN, but it seems like a reasonable alternative.
Indeed, rather than compare images, it's possible to just compare submission IDs, assuming FN stores the FA ID an image was imported from (I really hope it does!). Then this becomes a lazy as-others-import operation, same as how follows can synced as and when the people who follow import.