Thats absolutely possible via the underlying WebPayments API. The payment "wallet" is linked in the HTML (at least for web pages, RSS, podcast RSS, etc) so someone could design an app that reads these links as QR codes.
The whole point of WebPayments is that and payment solution that you (the "spender") wants to use which is compatible can be used to send money to any compatible wallet.
Whether the payment solution is via government backed, banking systems, or crypto, all it needs to be is compatible.
Its somewhat trivial nowadays to make a chrome extension compatible with firefox. I bet if you bother the dev of that site, they could get it done fast, especially since it's a relatively simple thing to do via an extension and I highly doubt it's using any WebExtension API's that aren't standardized between chrome and fieefox.
I'm switching to OSM, personally.
For android, OsmAnd is really solid and make editing easy. (Organic Maps is good too, but much less featured, depending on preferences.) I've started updating all the places I frequent and anything near me that I notice. Its actually kind of fun, to be perfectly honest. Its a small, somewhat selfless thing to do that has an impact on others around you.
IMHO, helping improve an open alternative for the community benefit is a far better act of resistance than a chrome extension that could easily be a GreaseMonkey script, aside from providing a bit of messaging.