They don’t have to install a browser, it’s already there.
And for those logged in to social media services at ALL times, yeah, they’ve got a lot of information on those folks. Thing is, they ALSO had a lot of information of folks that were NOT logged in to any social media accounts (as companies were using cross-site tracking technology to MUCH financial benefit without users knowledge). That avenue’s been cut, some of those German companies are seeing a drop in revenue and are taking action. (if those companies were NOT affected, this wouldn’t be an issue, so it can be said that Apple were quite effective!)