Do you know how they do it if the recipient is not participating? can the recipient claim the amounts later?
Are there options similar to what Brave is doing: adding a Tip button on sites like Reddit, Github, etc... (https://github.com/brave/brave-browser/issues/5040)
but for #lightning ?
An extension would be rather simple, I guess the challenge is to know the LNUrl for a given user.
Discussion
I think Brave knows who is participating since users signup for being a "publisher". That should be trivial with Alby, if you parse my profile's "social" accounts, you can see Alby. That could be the signal to trigger some buttons.
So the trick is mainly to decide where the info can be store publicly and parse that.