My saves vanished (again), but that just means I get to remake them (again).
It's still fun, but I can see this (eventually) getting annoying after a while, but for now, I don't care.
i recommend backing up your save files to your device! that way you'll always have access to them :)
here's how to do that btw:
first, click 'save to disk...' in the saves tab on the side menu. 
then, save your file as shown. 
to load in a disk save, click 'load from disk' in the same tab in the side menu.
click on the save you want to load in and voila! 
your saves are now backed up instead of localised to your browser cache :) hope this helps!