[Roodgorf]

But aren't you saying this is an already existing attack vector then?? Why try to find a similar one if you knew you could just get an older browser version and use this one? Is that not a good enough reason to be prepared for it?

[hcs]

As sagethesagesage said [1], you're protecting the user from having their browser pass the user's data from your site to a malicious site. The attacker shouldn't be able to make the user run an old, vulnerable browser.

[1] https://news.ycombinator.com/item?id=14282532