I thought I'd post a suggestion that I stumbled upon in my constant signing in and out, caused from having more than 4 yahoo teams.
For those of you who use Mozilla, if you get the IE Tab
Then what I have done, is log into your primary yahoo ID with Mozilla and then switch the rendering engine to IE via a right click on the tab and log into your secondary yahoo ID with IE.
I hope this saves someone some time and effort in checking all their yahoo fantasy baseball teams.
PS. I have no idea how to work three or more yahoo ID's, I'd say get a job