The other day, I finally got curious about the Site Specific Hacks option in the Develop menu of Safari. It turns out that browsers do their own hacks to certain known problem sites to make them work. Safari allows developers to turn off these hacks in the event that the developer is fixing a site that has hacks in Safari.
Opera, on the other hand, has a very advanced method for dealing with site specific hacks. It’s worth a read just so to know what kind of stuff goes on in the browser that most people, including developers, never think about. They also link to how other browsers deal with the problem.