Just copy this link and paste it into your browser:
Tumblr’s app is incredibly lame about links. I’ve tested it out on my own phone, and the link does nothing in the app but is fine on the phone’s browser (I have an old Android, myself). It’s also good on my Kindle’s browser.
So that might be why you’re having trouble – because you’re using the app. I’m sorry about that; I wish I could help you out more. Maybe one day Tumblr’s tech support will be better. 🙂