I’ve given this some though, and I think this is a stupid idea. I understand phishing is a legitimate security threat, but it’s one which requires user interaction at a higher level than most exploits. To prevent me from intentionally going to the Paypal website directly or from eBay is off-putting. It’s not a crisis for me to open Firefox when I want to use eBay, but it’s pretty crappy user experience if I have to remember to open one browser for one use case when I’d otherwise rather use Safari. I think this really boils down to me not liking a website/company telling me which browser to use.
I guess there’s naught that I can do but hope Apple includes support for Extended Validation certs in a (near) future version.