Dropbox folder does not seem to open

I think this is fine if you are only testing something for a few friends. However, there is an issue with using too much bandwidth if you try to host something through your public folder that becomes too popular. As per https://www.dropbox.com/help/45:

There are currently no hard limits on public bandwidth usage. We do, however, have an automated system for detecting and flagging unusual amounts of bandwidth usage. We will send an email notification whenever an account is flagged. Once flagged, public links will be temporarily disabled and users who use the links will see an error page instead of your file.

There's kind of a workaround. Add

?dl=1

at the end of the link that was shared with you. This will download the entire folder as a neatly zipped archive.

Note: This will not work with folders > 20GB or with more than 10,000 files.