hello, i think yahoo mail changed its interface recently. maybe you have to try to clear the cache & cookies from yahoo.com for the page to load correctly.

Yes, Firefox can display the tabs (see attached example from last Thursday).

I saw a screen shot with tabs missing in a different thread, although the main point of that thread was to solve the problem of some icons being replaced by a rectangle with two rows of two characters. Are you getting those rectangles as well?

If you use AdBlock Plus or a similar extension, create an exception for Yahoo or disable it temporarily and see whether that helps you. It helped a user in another thread whose Yahoo was not styled correctly.

Also, if you open Yahoo mail using an old bookmark, try navigating through the Yahoo home page instead.