[lazyjones]

> Even then the browser would still need to know to which websites the user could share. The user would first need to select websites and services they want to use.

They managed multiple search engine options just fine and mobile browsers implemented sharing without issues. I don't see a pressing need for user configuration (websites with share buttons don't allow this either), it would have meant potential additional revenue also for Mozilla & Co.

OTOH, they failed to fix "mailto:" for webmail ...

AFAIR toolbars added sharing buttons early on.