Yahoo Mail is still mostly tolerable in my book, but it weirdly insists on pretending that you can have multiple messages open at once in the same browser window. It's hard to describe if you're not using Yahoo Mail directly; basically, if you move your mouse pointer to the lower-left corner of the browser window, it tries to pretend that you've "minimized" everything.
It's a fairly useless feature and I'm partly convinced that it is a drain on the system (or related to the cause of "script on this page may be busy" errors in Firefox). The trouble is I can find no meaningful way of disabling it. I'm not even sure if I'm calling it by the right name.
Can someone possibly point me in the right direction?