Dave Hailwood - I just tried the link to your Board Horde game with Chrome and I just got a black screen after loading.
I have been testing a lot of prototypes on Dropbox this week, and I have had exactly the same issues with freezing, using both the http and https links.
I have noticed that it depends largely on the number and size of the images. Small projects work fine, but big ones don't.
I uploaded the same larger projects to Google Drive and saw a massive improvement. I think ultimately free web hosting is not the answer for big or complex games, still I'd say it's worth giving Google Drive a try
(Edit: Tried Link in Firefox and got to the title screen before it froze)