It's better to stick with open source stack. I like what Amazon is doing with AWS with services like RDS and ElastiCache. If one carefully selects the services on AWS, there is almost zero vendor lock in.
Google also had hiked the AppEngine price in Sept. 2011 which caused a lot of problems to early adopters.
This is a hard lesson each person learns on their own.
That's why I hate the whole SaaS idea - it turns products into services; something that should be permanent (as long as you can maintain the hardware it runs) into something that is ephemeral and ever changing. It's great for the service provider, but it totally sucks for the customers. SaaS drives entropy in the computing universe.
I'm not making a value judgement; I'm pointing out that SaaS is often picked for only its short-term benefits.
Link: https://events.google.com/io2016/schedule?sid=b4641ff7-0bef-...
https://www.firebase.com/terms/service-level-agreement.html
Though I think what you are looking for is Firebase being covered by a Deprecation Policy.
Which means you presumably saved months initially by using Azure, and got your product to market sooner. Everyone should be aware of the dangers of lock-in, and should carefully consider the value of it vs. the liability they're taking on. But I wouldn't say never use products like this. The value-add can be significant, even taking into account the fact that you may have to migrate off of it someday.