The all-new Yahoo! Mail uses several XML features (they are complicated but trust us, they help you) in the IE browser and in order to use those, you need to have Active X enabled.
Rest assured, there is no Active X download or installation of any kind. In order to utilize these special browser capabilities, please enable Active X with the following steps.
To enable ActiveX for IE 6.x and 7.0 for Windows: you can do the following:
You will see a scroll-down menu with radio buttons. Select the 'Enable' radio button for the following menu choices: