Say using Firebase AB Testing I'm testing if a layout built with columns performs better for keeping users in the app than a layout built with rows. Is it possible to ALSO test just for the users in the "rows layout" test whether users stay longer if there's 3 rows versus 4?
In other words, can I perform an AB Test, and also perform an additional AB Test on a subset of the users from the original AB Test?
If I understand your use case correctly, what you want is multivariant test, which Todd describes nicely in this answer.
If you want to have separate tests with overlapping users, this is not a built-in feature. Alternatively, you could do some workarounds like building audience of users in one variant - this is not something available in UI, your users would need to send some identifying event or set user property and then you can build audience based no that. Once you have audience ready, in the next test you can target only that audience.
