Hm. I personally haven't used Parse and I didn't even know they were with Facebook but I've seen it mentioned as a pretty popular back-end platform for Android apps (for example). What's the alternative then? AWS probably then?
I would not tie myself to a Cloud Platform but use open source stuff like docker which can be moved between Clouds. Btw, There's CloudBoost.io which is an alternative to Parse and is both on Docker (self-hosted) or as a managed solution at CloudBoost.io
Disclaimer: I work on Compute Engine, but not Firebase ;).