I saw this article posted over at Opera Watch.
As Daniel said, we see a lot of people complaining “xzy site works in IE but not in Opera.” Usually, this isn’t Opera’s fault rather it’s the fault of the web developers using in proper or non standard code. Sometimes, in the case of Microsoft’s MSN site and now Yahoo Mail, the problem is just discrimination.
Most people won’t take the time to look behind the code. They just assume it should work in everything. Well, when you send different code to one browser than you send to another, then yes, thing’s most likely aren’t going to work. In the case of Yahoo, they just decided not to send a good portion of the code.
Haavard Steen, a from Opera Software’s QA team has created a animated comparison between the code sent from Yahoo Mail to Opera and IE. Notice the difference?