I found a very helpful hint on some forum somewhere (Sorry, can't recall and can't find it) on changing the stupid new "not-quite-like-GMail" look of Yahoo Mail back to something close to the original style of Yahoo. Turns out, it's pretty easy if you know where to look!
While logged in to the new Yahoo Mail, point your mouse to the GEAR in the upper right:
From there, click the SETTINGS link to open up the Setting Panel. Once inside there, click on "Viewing Mail" on the left, then on "Basic" at the bottom:
When you are done, be sure to click SAVE.
This will not give you TABS back, but at least it breaks out the folders like it used to be, and I believe it gets rid of the stupid "conversation view" that Yahoo copied from GMail (which I hate).