We don't have a browser play option, but in general when folks have difficulty launching the game the most common issue is an antivirus freaking out. It depends on what antivirus you're using, but it's usually possible to whitelist a folder to say "things in here are safe". Our game does not contain any viruses, but it's obviously up to you to decide to fiddle with your antivirus if that's what causing the problem.
Edit: It's just occurred to me that if you're calling it an app you may be trying to download it from a mobile device. OBSCURA doesn't have a mobile version, if that's what's going on.