Which is easier said than done. For web traffic, the site has to use https for everything. Secondly, the site has to secure their cookies from being sent over h

Which is easier said than done. For web traffic, the site has to use https for everything. Secondly, the site has to secure their cookies from being sent over http, either by using HSTS with the includeSubDomains flag, or the "secure" cookie flag. Thirdly, you have to assume that the exit node isn't using a forged certificate from a compromised CA. Fourthly, you have to assume that the entity running the exit node doesn't have a zero day vulnerability for your browser, which they can deliver to you as soon as you make any http request to any site.