I must be special . Other than for a week or two a couple of months ago, I have consistently been able to see certificates, ecredits and lounge passes on my desktop using Firefox. I do not use the app other than for boarding passes and such, so I do not know about its functionality. When you are still not able to access this on your computer and you have done all you could on your end (switching browsers, clearing cache, etc.), I suggest you keep bugging Delta so they know the problem is not solved, at least not for you.