Except that Google's own statements are extremely clear that "leaked" (i.e. public) API keys should not be able to access the Gemini API in the first place: "We have identified a vulnerability where some API keys may have been publicly exposed. To protect your data and prevent unauthorized access, we have proactively blocked these known leaked keys from accessing the Gemini API. ... We are defaulting to blocking API keys that are leaked and used with the Gemini API, helping prevent abuse of cost and your application data." https://ai.google.dev/gemini-api/docs/troubleshooting#google...

For extra clarity on the exact so-called "vulnerability" that Google identified, see: https://news.ycombinator.com/item?id=47156925 This describes the very issue where some API keys were public by design (used for client-side web access), so the term "leaked" should be read in that unusually broad sense. Firebase keys are obviously covered, since they're also public by design.

(As for "Firebase AI Logic", it is explicitly very different: it's supposed to be implemented via a proxy service so the Gemini API key is never seen by the client: https://firebase.google.com/docs/ai-logic Clearly, just casually "enabling" something - which is what OP says they did! - should never result in abuse of cost on the scale OP describes.)