I am running 10.6. on OSX and Firefox 5.0.1. and cannot upgrade to the latest Yahoo Mail.
Error Message appearing on First Page:
You're almost there, but your web browser doesn’t support the newest version of Yahoo! Mail
Upgrade to a faster, more secure version of a supported browser. It's free and it only takes a few moments:
Firefox Internet Explorer (for Windows) Safari
Error Message on 2nd Page (when clicking the Firefox link):
Sorry, Mozilla Firefox optimized for Yahoo! is not available for your system.
The Yahoo! optimized version of Mozilla Firefox is only available for the following operating systems:
Windows 2000 Windows XP Windows Server 2003 Windows Vista Windows 7 Mac OS X 10.4 or later Linux
See the System Requirements for more details on hardware and software requirements and recommendations.